I think a fairly short period of testing for each piece of equipment should be enough. You can weed out the extremely unlikely DOAs that made it past the fab's QC that way, and any absurd error rates/slow hash speed/other problems can be discovered by the end users and exchanges can be worked out between the unfortunate party and Barntech rather than you and Barntech.

Much as I enjoy getting extensively tested, guaranteed to be good equipment, it doesn't make a lot of sense to delay everyone for the sake of catching a few possible problems.