I'm using these for P90X.  I love the ability to stack them.  I plan to buy some powerblock dumbbells at some point, but these bands allowed me to get started before making such a lofty investment.  I'll definitely also get the orange and purple bands.  Even after I get some dumbbells, I still think these bands will be a good change-it-up option, and allow me to do some exercises that dumbbells won't really be usable.