Quality of Pro Mags seems to be hit and miss. I don't have any for the Shield, but I do have a couple for my Bersa Thunder and Hi-Point 995TS. The ones I have just work. That doesn't seem to be true for everyone, though. Seems like it may just be a roll of the dice as to whether you get good ones or bad ones.
The Pro Mags (10 round only - I haven't tried the 15 rounders which have VERY bad reviews) for the Hi-Point seem to be better quality than the factory mags. I know that's not saying much since magazines tend to be the achilles heel of that particular weapon.
So . . . I only buy Pro Mags if they are the only magazines I can find at the time and I desperately need or want additional magazines. I guess I've been lucky so far.
The only really useless magazine I've ever bought was from a company in California that makes mags for long discontinued weapons. I can't remember the name of the company, but at the time I desperately wanted an extra mag for my kid's Winchester 77. They are about as rare as hen's teeth. It took awhile, but the $49 plus shipping mag arrived . . . and it will not feed. PERIOD. Total junk. I did manage to pick up an additional factory mag on gunbroker, but it was not cheap. Cost me nearly $100 with shipping. It works, though.