buy these after begin p90x . they be perfect for program such as p90x because you do so many different exercise during the workout , that you absolutely must have the ability to quickly change weight . the weight themselves be build solid and will last a long time . the simple selector pin setup be very easy to use , and make add or reduce weight a 5 second event to change both dumbbell . the weight themselves look a bit bulky and clumsy since they be square\/rectangular shaped , however they be anything but . I would recommend these weight to anybody that be look for a reliable set of adjustable dumbbell . I originally be go to purchase the Bowflex brand , until I read too many review from people say that the plastic lock mechanism break on theirs at least once and be not the cheapest thing to replace . the only thing on the PowerBlocks that can really fail would be the selector pin , but its a simple piece of heavy duty plastic . I dont foresee it break anytime soon either ... a one sentence synopsis of the powerblock ? `` a simple , functional , solidly build set of weight that will not dissapoint '' .