This means that you can work out without unnecessary breaks in a convenient and efficient manner. The best way to choose which one is the right one for you would be to read what others have to say.
There are hundreds of reviews about adjustable dumbbells who will give you a pretty good idea which ones are worth your money. I have read quite a lot of them and it seems that most of the reviews have one thing in common. People either advice to stay away from adjustable dumbbells and save your shelf some money by purchasing ten or more sets of non-adjustable dumbbells, or they suggest to carefully selecting only the best ones.
There is no point buying adjustable dumbbells if their system is not easy to use and it takes more than a few seconds to switch weight.
Also if they are not made from top quality material the dial mechanism could fail and leave you frustrated without any set of dumbbells that work.