He's a GM Carry Optics competitor that shoots the Rival platform. If you haven't heard of him, you will soon enough.
As for the 5 star review, some people are quite literally getting theirs from the first batch of production. I'm sure there will be plenty of reviews in due time.
To those concerned about slide lock...this thumbrest is machined without that feature deliberately. To clarify, you can run a magazine dry...and the gun will not go to slide lock. It will cycle and return to battery. For most of us, this isn't an issue considering we've been running aftermarket followers that won't bring us to slide lock either.
As for those concerned about the positioning....I genuinely just suggest trying it out. I think you'd be pleasantly surprised.