these be exactly what I want for my p90x experience . they be affordable and sturdy , unlike some other cheaper adjustable dumbbell I look at . I find no trouble at all in change weight quickly . I be able to change they on carpet without issue as well -lrb- although my carpet be not plush , so I would assume that situation would be remedy with a piece of cardboard or wood -- stand be not need in my opinion unless you want they up higher -rrb- . my only minor complaint be the handle be smooth . again , not a problem for I since I wear glove , but if I do not have glove , the smooth surface would make they slide in sweaty hand . the block feel natural and balanced , so I be overall extremely pleased . not as `` sexy '' as the Bowflex model , but certainly a much better deal price-wise .