I bought a pair of Bowflex SelectTech 552 Dumbbells a couple years ago for my home gym. For the most part I am quite pleased with them. Although I am writing about this specific brand of adjustable dumbbell set, I am sure much of what I say can be applicable to all of the different brands.
The first and most obvious advantage is the space savings associated with the Bowflex SelectTech 552 Dumbbell set. It's simply not feasible to have over a dozen pairs of dumbbells at different weight increments cluttering up your home. Also, it's a lot cheaper to buy an adjustable dumbbell set over buying each pair of weight increment individually.
Another great advantage is that the weights do not damage easily. Over time, other dumbbells will start to erode or have surface chipping with use. That makes those dumbbells ever so slightly lighter than their posted weight. With this weight set you know that a 30 pound dumbbell is actually 30 pounds. Also, you won't have paint chips or rust dirtying up your hands every time you handle these weights.
But by far my favourite advantage of the Bowflex SelectTech 552 Dumbbell set is the ability to have uneven weight on each side of the dumbbell. For instance, if you wanted a 30 pound dumbbell, you could set each side to the 30 setting so that 15 pounds of weight sits on each side of the dumbbell. Alternatively, you could set your weight to 30 by having one side set to 25 and the other to 35 so that 12.5 pounds of weight sits on one side and 17.5 pounds sits on the other. I find the ability to do this very helpful for Bicep Curls and Forearm Curls as it hits the muscles in a very different way than curls being done with a normally distributed dumbbell.
The main disadvantage to the set is that while as a group they save a lot of space, but as individual weights they are much more bulky. Because of the way they are designed, a dumbbell that's 5 pounds is the same length as a dumbbell that's 50 pounds. And both the 5-pounder and 50-pounder are bigger than a standard 50 pounds dumbbell.
This can wreak havoc on your range of motion during certain exercises. It's nearly impossible to do front dumbbell raises as the one moving upwards will always collide with the one moving downwards. I find them to be an inconvenience when doing Dumbbell Bench Presses and Shoulder Presses as well. The weights are also more likely to interfere with your leg while doing Dumbbell Bicep Curls though I find this to not be much of an annoyance.
Despite the disadvantage that interferes with your range of motion, I still highly recommend these dumbbells for anyone who wants to expand their home gym.
Refer to my other workout articles if you are interested in:
How to build big Biceps
How to build big Triceps
How to build big Forearms
How to build big Shoulders
How to build a big Chest
How to build a big Back
How to build big Legs
How to build big Calves
My Workout Routine
More of my workout advice:
Are Bowflex SelectTech Adjustable Dumbbells suitable for you?
Should you buy Bowflex SelectTech Dumbbells in a store or online?
Why you would want to use barbells for your workouts
Why you would want to use dumbbells for your workouts
How I lost over 40 pounds in 6 months with some simple diet changes
Upper body exercises with no equipment needed
Lower body exercises with no equipment needed
Cardio exercises with no equipment needed
The Different Ways of Doing Dumbbell Bicep Curls
Inflatable Exercise Ball Exercises for Men