I just bought these sights as well. I put them on my Extrema and I kinda like them. I like the way they look as far as sighting down the barrel is concerned. I'll be honest with you though, I'm just a little skeptical about the plastic spacers. I followed their directions and they seem to be on the gun very solidly but....I'm not a fan of anything on the gun, especially the sights, being plastic. Their directions said that the plastic spacers were optional, but without them the sights will definitely fall off. I don't think the allen bolts can tighten that much without bending or snapping.

I put some "witness marks" on the rib of my gun and will keep an eye on the sights to see if they slide or shift when I go pattern soon.