I've used some ProMags over the years. It seems that when they fail it's due to mediocre springs. Replacing the springs typically leaves you with a good mag, but buying the springs offsets any savings you might enjoy when buying them at their generally lower price.
Back during the Clinton magazine ban, CZ announcd a 75 B Compact in 40 -- but never built it. Promag made the mags, and they worked like hi-cap mags in 9mm guns but held 14 rounds rather than the 9mm 10 rounds. The ATF said they were legal, so they became very popular for CZ Forum users for a number of years. (The fact that CZ later had a lot of problems making a .40 compact mag that worked made the Promags even more popular.)
I've also had a couple of Promags for a Beretta 92, and a couple for a S&W Model 59 that worked in the DaeWoo DP-51, when mags were hard to find for that gun.
Using Promags is likely to be a crapshoot, but some of their mags work well for some gun lines. But...
Because there are generally Mec-Gar mags (the gold standard for magazines) and their prices are seldom more than a couple of dollars higher than Pro Mags for the same gun, I'd only buy a Promag if I needed mags for a gun and culdn't find them anywhere else.
That said, if I get another compact (metal-framed) CZ, I wouldn't hesitate getting a .40 mag for my 9mm compact.
