As far as I know, a Strat sounds better if the trem block is a bigass heavy lump of steel.
If you have a Strat with an aluminium or diecast zinc trem block, then it might be worth upgrading to a steel one, because these metals are much lighter than steel.
I think the American series Strats have a steel block already, though. Mine seems to, but of course Callahan claim that it's made of poor quality cast steel and their cold rolled one is superior. I'd guess hood ornament, and an invisible hood ornament at that, unless their block is actually bigger and heavier.
But then, I guess with their Delrin bushing system you don't need to worry about losing the little spring.
And their steel Tune-o-matic bridge is very sexy. I was always suspicious of the zinc ones.