Hmmm, one thing I've learnt to my peril is that they're one use only. If you bang a new one on and leave it it'll last the life of the chain. If you remove and re-fit them to change out derailiers, clean etc they go pop.
It's important to remember that the 10 speed version is called 'powerlock' as opposed to powerlink and is not reusable. I know this is the MTB forum so probably not relevant, but a point worth making I think