The PowerBlock Elite dumbbell weight plates are a mix of 2.5 and 5 lbs increments, ranging from 5 to 50 pounds. After you've reached the point where 50 lbs seem too light, you can buy an expansion, increasing the weight up to 90 lbs. You can use these for both strength and conditioning exercises, and they will last for a long time.
There is no fancy mechanism - you just pull a metal 'fork' out of each dumbbell and place it where you need to. The weight plates are color coded, and correspond with a color coded chart on the side of each dumbbell. It might take some getting used to, but once you're familiar with it, changing weight plates would take about 5-10 seconds for each dumbbell.
There are no moving parts that would break with misuse, and the construction of these dumbbells is solid and stable. There is also a 10 year home use warranty, which is considerably more than other options (most offer 2 year warranty).
If you've done, for example, 3 reps of your workout and you want to change the weight of your dumbbells to less, your hands could be a bit shaky at this point. This would make inserting the adjuster 'fork' more fidgety than with a dial, but it's not a dealbreaker.
These dumbbells have a dial-adjust that allows you to change the weight in about 5 seconds in between reps. This is great, because your hands will get shaky after some time of lifting, and after just turning the dial you can spend your break actually resting, instead of fidgeting with your dumbbells to get ready for the next rep.
The Bowflex SelectTech552 dumbbells are a good investment for people who want both strength training and conditioning. Their length forces you to use your stabilizer muscles a lot, which makes for a better (harder) work out in both strength training and conditioning. It's very easy and quick to change the weight on these, which is important for conditioning workouts.
Because of their dial-adjust mechanism, the Bowflex SelectTech 552 is a great investment for people who want to work out at home, but don't have the space for a home gym. Given the number of increments these dumbbells have, you'd need 14 separate dumbbells to cover you from 5 to 52.5 lbs.
You can change weights in 2.5 lbs increments, starting from 5 lbs up to 52.5 lbs. This gives you a lot of control over any stage of your workout. Combine this with the ease of using the dial-adjust, and you can fine-tune these dumbbells to suit your every need without frustration.
Bowflex stands out from the competition by providing instructions for picking up/putting down their dumbbells in a safe and sustainable way. It's encouraged that you read these instructions and follow them, because that will help you avoid injuries and increase the lifespan of your dumbbells. This shows concern for their users well-being, and gives some peace of mind to beginners who are worried about working out without a personal trainer.
The trays (need to be purchased separately) for the Bowflex are set up so that you need to be mindful when placing the dumbbells back. All weights need to be lined up for it to fit, which takes an extra second or two of concentration. Furthermore, it's not recommended that you drop these weights from more than a 12 inch height. You should instead adjust the weight to a lower setting, to eliminate the need to drop them if your muscles get fatigued.
The StairMaster TwistLock dumbbells are a great (but expensive) option if changing weights as fast as possible is the most important thing. These dumbbells use their handles as the primary mechanism for adjusting weight. Just place the dumbbell in it's tray and twist the handle. It's a good time saver for very fast paced conditioning workouts. The mechanism only works when the dumbbells are docked in their trays, so you don't have to worry about anything going wrong in the middle of your workout.
These dumbbells go from 5 to 50 lbs in 5 pound increments, which is a great place to start for someone just starting out. It's not as customizable as some other adjustable dumbbells, but it's still good.
It could be that with any mishandling or heavy use the metal pin that catches and releases weight plates could fail. These dumbbells have a lot of non-metal parts, which also add to the uneasy feeling about their durability.