BowFlex SelectTech 840 Kettlebell Review: Six Weights in One Bell

The BowFlex SelectTech 840 is a dial-adjustable kettlebell that replaces six fixed bells, from 3.5kg up to 18kg. It's a good buy if you want fast weight changes and a small footprint for swings, goblet squats and presses at home, and a poor one if you want a bell that feels and handles like cast iron. At £141.99 on Amazon UK at the time of writing, it costs about what two or three mid-weight fixed bells do.

The idea is simple. You sit the bell in its base, turn a dial to the weight you want, and lift out the handle with only those plates attached. No tools, no spanners. BowFlex's own spec page lists six weights (3.5, 5.5, 9, 11, 16 and 18kg), a 2 year parts warranty and a bell body that measures 22.4 x 17.8 x 31.8cm.

The trade-offs are just as clear. The shape is bulkier than a cast-iron bell because the plates and selector live inside a plastic-shelled body. It isn't built for juggling or high-rep snatches. And without the base, you can't change weight at all.

Who it is for

The 840 makes sense for a few kinds of buyer.

• Beginners who don't know their weights yet. Starting at 3.5kg, it covers halos and light presses, and 11kg or 16kg works for a first swing.
• Shared households. Two people can use very different weights without swapping bells.
• Small spaces. One footprint instead of six.

It's a poor fit if you already swing 20kg or more, since the top setting is 18kg. It's also awkward for anyone who wants fine jumps for progressive overload, and for anyone who'll be dropping, throwing or juggling the bell. Not sure what weight you need? Our what weight kettlebell should I use guide gives starting weights by exercise.

The weight steps

Six settings sound flexible. Look at the actual numbers though: 3.5, 5.5, 9, 11, 16 and 18kg. The gaps are 2, 3.5, 2, 5 and 2kg.

That 5kg leap from 11kg to 16kg is the one that matters. Plenty of people find 11kg too light for swings and 16kg a reasonable target, and the BowFlex gives you no middle. Presses, windmills and get-ups suffer most, because a jump that size can mean going from comfortable to unmanageable in one step. For swings and deadlifts it's less of a problem, since you can use more reps or slower tempos to bridge it.

Compare that with the Bells of Steel adjustable kettlebell, which runs 12 to 32kg in 0.5kg steps. It's a different animal: a steel competition shell, around £300, tools needed. If you expect to progress past 18kg, it's the better long-term pick. If you want quick changes and light weights, the BowFlex wins.

Shape, handle and build

A cast-iron kettlebell is a solid ball with a handle. The BowFlex is a plastic-shelled body wrapped around the plates and selector, and that changes how it sits and moves. It's wider and chunkier than a fixed bell of the same weight, so the rack position, where the bell rests against your forearm and chest, feels different. People with smaller frames report the bulk sits awkwardly, which is a common complaint with dial-style bells.

The 22.4 x 17.8 x 31.8cm footprint is BowFlex's own figure. We haven't seen a published handle diameter, so we won't guess one. Check the owner photos on the Amazon listing and compare against what you're used to before you buy.

What we're confident about is the design limit. The plates sit loose inside a plastic shell. That's fine for swings, squats, deadlifts and presses done with control. It's the wrong choice for juggling, throwing or high-rep snatches, where the bell lands or rotates fast. And you shouldn't drop it. A cast-iron bell shrugs off a floor slap, but an adjustable selector mechanism is more likely to take damage.

Kettlebell work itself is well supported by research, though no study used this bell. In a 6-week trial, twice-weekly kettlebell swing training improved half-squat strength by 9.8% and vertical jump by 19.8% in 21 healthy men, with no significant difference from jump squat training. Another randomised trial found that 8 weeks of ballistic kettlebell training reduced musculoskeletal pain in workers with high pain levels. The first used 12kg or 16kg bells depending on body mass, both inside the BowFlex's range. If swings are your main goal, see our kettlebell swing guide.

Using it day to day

The dial is the selling point, so it's worth saying where it pays off. Picture a 20 minute circuit: goblet squats at 16kg, halos at 5.5kg, then a few presses at 9kg. With fixed bells you'd have three on the floor. With the BowFlex you return the bell to its base, turn the dial and lift out the new weight. It takes a few seconds, and nothing sits around to trip over.

Where it frustrates is anything that needs a precise load. If your last set of presses at 9kg was easy and 11kg is too hard, you're stuck. Many lifters get round this with extra reps, slower lowering or a pause at the bottom, which works but isn't the same as adding 1kg. Swings forgive the gaps better than presses do, and for general fitness that's often enough. Anyone chasing a specific press target, such as a strict 16kg overhead, will want a bell with finer steps.

Storage is simple: the bell lives in its base, and the pair fit on a shelf or in a corner. Keep the dial set to your lightest weight between sessions so the next person doesn't lift an unexpected 18kg.

The drawbacks, honestly

It's bulkier than it looks in photos. Because the selector mechanism lives in the body, the bell is bigger than a cast-iron bell of the same weight. Expect a wider footprint on the floor and a clunkier feel in the rack.

Not for juggling or high-rep snatches. If your plan includes snatch ladders, bell flips or anything that sends the bell spinning around your hand, buy a fixed cast-iron or competition bell. The BowFlex is a swing-squat-press tool.

Rough drops are out. Set it down, don't let it fall. Once weight is dialled in and the handle is lifted out, it's a sealed unit, but it isn't a bell you slam to the floor.

The base is non-negotiable. Every weight change needs the base. That's no hassle in a home gym, but it's one more object to store, and it makes the bell awkward to take to a garden or a friend's house.

The 5kg jump. Already covered, but it's worth repeating because it's the most common reason people outgrow this bell early.

Ceiling of 18kg. Many men and a fair number of women will want 20 to 24kg for swings within a year of consistent training. At that point you're buying a second bell.

Value

£141.99 isn't cheap for six weights. Three fixed bells in the mid weights will often cost less than that, but you'd get three weights, not six. You're paying for six weights in one footprint and a dial that changes in seconds.

If you'll use three or four of those weights regularly and space is tight, the maths works. If you'll only ever use one or two, buy fixed bells.

Check today's price on the BowFlex SelectTech 840 kettlebell£141.99

Alternatives

• Bells of Steel adjustable (12 to 32kg). Heavier, more precise and tougher, but tools are needed and it costs roughly twice as much. Read our full Bells of Steel review.
• Other adjustable kettlebells. Our adjustable kettlebell guide compares the main designs, including cheaper plate-loaded options.
• Fixed bells. Still the simplest answer if you need two or three weights. See our best kettlebells UK roundup.
• Adjustable dumbbells. If you'd rather build a whole home gym around selector tools, dumbbells give finer steps and a more natural grip for presses and rows.

See the BowFlex SelectTech 840 on Amazon UK£141.99

Recommended reads

• Adjustable kettlebell guide: how the main adjustable designs compare
• Bells of Steel adjustable kettlebell review: the heavier, tool-based alternative
• Best kettlebells UK: our fixed-bell picks
• Kettlebell swing: technique and programming for the core lift
• Home gym: more strength kit for small spaces