+1 on the polymer Magpul ... They make aluminum ones also
I have put several things from Magpul on my ARs like: the B.A.D. Battery Assist Device, the Ambidextrous Sling Attachment Point, and the angled forward grip. I have had zero issues.
The only reason I replaced my trigger guard was because mine had a sharp edge on it. I don't shoot with gloves on.