Now, before you all start booing and hissing, hear me out.

I've been doing some research and it seems that the Promag 32 round mag for CZ pistols is actually not bad, and with a CZ follower it's pretty reliable. Now, is there a similar case for the Browning Hi Power? I cannot seem to find any information, accounts, reviews, or anecdotes about the Promag happy sticks for the BHP, whereas there are a few for the CZ. If I bought a promag happy stick for the BHP and used a Browning/FN/MecGar follower in it would it be reliable?

Thanks for the time.

If you have a choice, take one of your reliable BHP mags with you when you buy.  Compare the feedlips geometry with the promag and get the one that is closest.  You can always do minor re-shaping as needed.

Or you can just buy the 20 round Mecgar mags.  I've got one that I bought in early 1994 and it works every time I use it.