Thinking of buying adjustable dumbbells?

If you're looking to add some dumbbells to your home workout routine, fixed-weight models are the cheapest way to go. (We discuss the various options in our new report on dumbbells.) But the problems are obvious: When you're ready to graduate to heavier weight, you have to buy new ones, and if you'd like to use dumbbells for both upper and lower body exercises, you'll likely need several sets in various weight increments.

With adjustable dumbbells, you can add or subtract weight, so they take up less room and can grow with you. But there are a few things you should know before you buy.

Selectorized dumbbells, which are commonly referred to as adjustable dumbbells,are the type you see most often in stores. These dumbbells work much like weight machines you may have used in the gym, where you slide a pin or turn a dial to select the weight desired. When you lift up the dumbbells, the selected weight remains on the bar, while the excess weight remains on the stand or floor.

Adjustable weights, while expensive, can be cheaper than buying a full set of fixed-weight dumbbells. They're compact and convenient, but they also have small parts and can break easily if dropped. As a result, they have shorter warranties than fixed-weight dumbbells, typically only a few years. It can also take some time to swap weight plates, especially if you need to change weights between each exercise.

Overall, we found the best reviews for the Bowflex SelectTech Dumbbells (*Est. $400 and up). They're consistently the highest-rated dumbbells on user-review sites, and they earn recommendations from several fitness publications. The Bowflex dumbbells come in two versions: the SelectTech 1090 adjusts from 10 to 90 pounds, while the SelectTech 552 ranges from 5 to 52.5 pounds.

One set of dumbbells you might want to skip are Aquabells (*Est. $50). Often marketed as travel dumbbells, Aquabells must be filled with water. They weigh only 26 ounces when deflated, and they can weigh up to 16 pounds per dumbbell if you fill up all four "weights." However, the inflatable sections of the Aquabells have very small holes, so you must use a thin stream of water to avoid making a mess.Unless you really need a solution for travel, other products are better.

Check out our new report on dumbbells for more on both fixed-weight and adjustable models.