if the masterlink broke, it was not put on correctly.
They are very easy to install incorrectly. I'd say about 80% of the masterlinks I see are installed incorrectly.
I am running a no name cheap 530 chain, no problems whatsoever. I've never broken a chain, for that matter. Tensil strength is kinda a joke IMO. my "cheap" chain has a LOW rating of 8500, for humor factor, I once calculated what that absolute most psi I could ever see at the chain. I came up with 1200, and that was a) assuming I geared my bike way down, b) ran way higher boost than I normally do and c) could actually use full throttle in first gear.