I have the AA magwell on a G19. I don’t shoot competitively so I can’t speak to its usefulness or how many tenths of a second it saves. I can say it is a really well made piece. No regrets there. Magpul makes a $20 version in plastic err polymer but it doesn’t look nearly as good.
So basically I like it a lot but can’t speak to anything else
I have both, taran tactical extensions and agency magwell for my 19. They work together perfectly. No issues from my end. The magwell works perfectly especially for CC. I'd much rather have an agency magwell than one of those big, clunky magwells.
I also just ordered a magpul magwell the other day for my 17 Gen 4. I don't believe they have one for the 19 yet. But I think they are in the works. And at 1/4 the price.