Ask them what coating they are using and what the tolerances are between their barrel and pistons as well as if they are a matched set or batch runs.
An upgraded spring to accommodate for the extra mass is important as well and new seals of a high enough resistance to fuel are needed too.
If its a stepped piston and does not include a new retaining nut, I would be concerned as that won't allow for upgraded seals usually.
but if they hit on all of those items, its more than likely pretty good assuming the manufacturing is Six Sigma. Ask them that too.
