azzle123:
His arms are about the size of my thighs 
And Stuart...they have a lifetime warranty so if your spinning away and it flys out your hand and smashes into bits, they'll give you the parts to fix it!

they only replace them if they have not been dropped, that seems to be the problem with all mine sooner or later they get dropped and it makes a mark in the plastic case, then onece the metal axis has smoothed out the mark it has kless grip overall. they sent me a few poly rings once as i managed to wear one out without dropping it, but the majority of mine all have knackered platic spheres
and i've tried an ironball they are not as good, IMO they spin too fast without exerting much gyroscopic force, you need to get it to about 13000 just to feel a burn and thats hardly the sort of speed you can maintain