Looks legit. I see you went the o-ring route. I just finished doing one the same minus the sweet coated pistons. Hard to believe how much .005 of push against the gasket helps
The way Guy explained it to me was the fire ring method has a groove in both surfaces and there's a ring that sits in the groove. You then get a head gasket that goes outside the ring and the ring keeps the fire away from the gasket.
O-ring has a .035 groove in the block and uses a .040 wire like you see in the bag in the picture. That method uses a regular head gasket and just has extra pressure right where the fire ring sits. Both are supposed to hold up well with high hp and boost.
As far as disadvantages I wouldn't know any. I think anything you can do to keep from having to tear a fully built motor apart is a no-brainer