I notice that some reviewer -lrb- the one rating the PowerBlocks the lowest -rrb- be talk about a completely different model . this set do not have `` interior weight '' and you do not remove weight in the handle to switch between any weight and the next one you want . with this set , all you ever do be slip the pin from one weight to the next . for p90x it be good to be able to change weight fast , so this be a good set to get . also , the weight range be great and will perfectly suit almost every excercise , except you may have to do a few extra rep on the row -lrb- `` lawnmower '' -rrb- . the set be as compact as dumbell of the same weight , so you can do curl without bang you leg . if you pick a lighter powerblock weight , the weight be shorter , more compact , than a bigger weight , just as regular dumbell would be -- unlike other brand where you still have a long handle with a tiny weight . other PowerBlock model do use handle weight which can slow thing down , and be not the best pick for p90x . you can identify these set by they description , or by the picture which will show the include , silver , cylindrical add-in weight . my own set be a older model that go 5-50 lb in 5 lb increment . in any case a adjustable set be very economical . regular dumbell cost around $ 1.20 a pound -lrb- gray , tube handle -rrb- or $ 2.20 a pound -lrb- black , rubber coated , shaped handle -rrb- . so a set go from 5 to 45 pound in 5 pound increment would run $ 550 - $ 1000 a set . nevertheless , if you have both space and money , a complete set of regular dumbell be the best , safest , fastest , and most flexible of all . I have a full set at one house , and a powerblock at the other . they both do the trick .