I thought I posted this a while back, but can't find it, so...
I've always trusted the Wix quality though lately I've been using Baldwin B2, which has the same construction as Wix 51515. At a cost of $4-$6 you'd be hard pressed to do better, IMO.
The reports I've read of dissected genuine aren't very impressive. The Cooper I opened, who supposedly make the genuine, wasn't impressive at all. Both have the bypass in the dome end.