Congrats on your 4516-2! One of the best compact 45's out there IMO.
The black follower mags were the last issue for the 3rd gen 45's. They were the standard issue on all of the last LE contract 3rd gens too.
I have shot various 4516's over the years using all the different FACTORY mags, red/orange and yellow followers, and never experienced a failure to feed or stopage.
That said, I only use the latest - black follower - mags in my for serious S&W 45's.
I would not have a problem with Mec-Gar for range/competition use but would NEVER use a Pro-Mag for any purpose. They are junk in my experience. Hope this helps! Enjoy that 4516-2!
We like range reports too!
Regards 18DAI