Adjustable kettlebells solve a specific problem: you need multiple weights but don't have room for six fixed kettlebells. The JAXJOX KettlebellConnect 2.0 adjusts digitally from 12 to 42 lbs in 6-lb increments and connects via Bluetooth to track reps and sets. The Bowflex SelectTech 840 goes from 8 to 40 lbs using a lever mechanism. Both are considerably more convenient than a full kettlebell rack. The question is whether either one feels like a real kettlebell — and neither is perfect on that front.
Bowflex SelectTech 840
The Bowflex SelectTech 840 is the better all-around adjustable kettlebell. Its lever mechanism is faster to adjust, the shape is rounder and more traditional, and it handles swings, cleans, and Turkish get-ups with fewer complaints than the JAXJOX. The JAXJOX's Bluetooth rep tracking is a clever feature, but not worth the trade-offs in adjustment speed and cost for most buyers.
Specs Comparison
| Spec | JAXJOX KettlebellConnect 2.0 | Bowflex SelectTech 840 |
|---|---|---|
| Weight Range | 12–42 lbs | 8–40 lbs |
| Increments | 6 lbs | 5 lbs |
| Adjustment | Digital dial | Lever |
| Bluetooth | Yes (rep tracking) | No |
| Shape | Rectangular block | Rounded (traditional) |
| Price | ~$229 | ~$179 |
Shape and Swing Feel
Traditional kettlebells have a round, consistent shape that balances predictably during dynamic movements like swings, snatches, and cleans. The JAXJOX KettlebellConnect has a blocky rectangular profile that many users find awkward during swings — it doesn't move through the air the same way a traditional bell does. The handle is good, but the overall shape is a compromise.
The Bowflex 840's shape is closer to a traditional kettlebell — it's still not identical to cast iron, but the rounder profile handles swings and cleans more naturally than the JAXJOX. Users on r/homegym who do kettlebell-specific training (RKC-style swings, get-ups) consistently prefer the 840's ergonomics.
Adjustment Mechanism
The JAXJOX adjusts via a digital dial on the handle — you twist to the desired weight and it clunks into place. The mechanism is clever but slow: 3–5 seconds with some fiddling. The digital display shows the selected weight, which is convenient. The internal stacking mechanism is reliable but adds bulk.
Bowflex's lever system adjusts in roughly 2–3 seconds by turning a lever at the base. It's physically faster and more intuitive. During circuit training where you're switching weights between exercises, the Bowflex mechanism's speed advantage compounds. Neither mechanism is as fast as picking up a different fixed kettlebell.
Bluetooth Tracking
The JAXJOX's defining feature is Bluetooth connectivity to the JAXJOX Coach app, which uses the accelerometer in the kettlebell to count reps and track workout data. In controlled tests, the rep counting works reasonably well for consistent movements. For swings and goblet squats, it's accurate. For get-ups and asymmetric movements, accuracy drops.
The Bowflex 840 has no connectivity features. It's a mechanical weight adjustment device with no sensors. For athletes who already use a GPS watch, phone, or other tracking app, the JAXJOX's built-in tracking is redundant. For beginners who want guided workouts, it's a nice-to-have.
Weight Range
The JAXJOX starts at 12 lbs and tops out at 42 lbs in 6-lb jumps. The large increment size (6 lbs) can be frustrating when you're progressing between weights — the jump from 24 to 30 lbs is significant for some exercises. The minimum of 12 lbs limits use for lighter movements like halos or beginner work.
The Bowflex 840 starts at 8 lbs and goes to 40 lbs in 5-lb increments (8, 12, 18, 25, 35, 40). The 8 lb starting weight makes it more accessible for beginners and useful for lighter conditioning work. The increments are similar to JAXJOX but the lower starting point is an advantage.
JAXJOX KettlebellConnect 2.0 Strengths
- Bluetooth rep tracking and accelerometer in the kettlebell
- 42 lb max — 2 lbs heavier than Bowflex 840
- Digital display shows selected weight clearly
- JAXJOX Coach app guided workouts
Bowflex SelectTech 840 Strengths
- Rounder, more traditional kettlebell shape for swings and cleans
- Faster lever adjustment mechanism
- Starts at 8 lbs — better for beginners and lighter work
- Lower price (~$179 vs ~$229)
JAXJOX KettlebellConnect 2.0 Weaknesses
- Rectangular shape feels awkward during dynamic movements
- 6-lb increments — coarse adjustment for progressive overload
- 12 lb minimum limits lighter conditioning work
- $229 + optional app subscription
Bowflex SelectTech 840 Weaknesses
- No connectivity or rep tracking
- 40 lb max — slightly lower than JAXJOX
- Shape still not equivalent to cast iron kettlebell
Best For
- a: Tech-forward buyers who want automatic rep tracking and guided app workouts built into their kettlebell
- b: Kettlebell athletes who prioritize traditional swing mechanics, faster adjustment, and lower cost
FAQ
Can adjustable kettlebells replace a set of fixed kettlebells?
For most home gym users, yes. If you're doing RKC-style training with competition bells at specific weights, you'll notice the shape difference. For general fitness and conditioning, adjustable kettlebells cover the range adequately.
Is the JAXJOX rep tracking accurate enough to rely on?
For two-handed swings and goblet squats: yes, it's reasonably accurate. For one-handed movements, Turkish get-ups, or unconventional exercises: less so. It's a nice feature, not a precision tool.
Which adjustable kettlebell is best for kettlebell sport (IKFF/AKA)?
Neither — competition kettlebell sport requires fixed-weight, competition-spec bells with specific handle diameters and tolerances. Adjustable kettlebells are for general fitness, not sport-specific competition training.