I had one on my '65 SS. It was cracking from when I got it in 1996. I finally had enough of it's ugliness and removed it. I will be filling in the 6 holes when I pull the windshield for a bit of rust repair at it's base very similar to what's seen in the pic above.
Everyone I've seen always looked like it was some kind of afterthought. The corners facing the passengers always turned up. Not sure if it would do anything to save your face in an accident anyways. The dash top painted a nice gloss would look so nice.
1965 Impala SS, 383, 4 spd
1970 Caprice LS-4 454, TH400