I hate to quote people, especially when I have to paraphrase.
Let's say I talked to a guy who has been PROOFING .475 and .500 Linebaughs for a few decades who told me the only aloy grip frame he broke with a proof load was when he didn't bother to put a in second screw (much less the 3rd, 4th & 5th). Apparently his kid was making grips for the bisley grip frame for the gun and he didn't have it to hand, so he just bolted on a stock alloy one to proof it.
They are perfectly fine with all 5 screws.
I don't care for them for the balance, and typically the finish.
Of the (umm, less than 20 now) Ruger SA's I still own, not a one has an alloy grip frame.