Get the Dumblers, as a set!
You need a set, let's get that straight now.
The handle and locking mechanisms are the foundation of any dumbbell (or barbell for that matter). The quality of the construction of The Dumbler is the best I've ever seen, and held, and if you're reading the reviews, you're probably most interested in the magnetic locking mechanism they use. It works great. Like hang it over your head and don't sweat it, great. The notches are deep and absolutely add security to the sliding lock plate. Next to that, it's a very low-profile design, making it easy to use without snagging your clothes, is good for transportation, and for storage. Knurling on the handle is equally as great.
I looked at many types of dumbbell bars and adjustable dumbbells before I settled on The Dumbler, and I couldn't be happier. If you're like me, and have been aching to add onto your home gym equipment, but want to ensure you're getting the best stuff, spend more of the budget on these foundational pieces, and buy used plates cheap secondhand. Safety first!