I want to expand on this just a tiny bit in fairness to ProMag...
ProMag for Desert Eagles have fundamental design issues in my opinion. The ones I have don't work and getting them to work, in my opinion requires a design change.
However... but this is not the case for all firearms... kind of. I bought a 32 Round ProMag for a Sig P320 because they were $17 and my factory 21's are $50+. In on-line research, sometimes these 32 round magazines would barely work, but some videos and testimony showed mag-dumps one after the other with no issue.
So I bought one...
Sure enough, there is really no design flaws in them that I see, but the finish and fit was just poor. I first cleaned all of the black oil off the inside of the magazine and spring, and it still seemed rather rough. Looking at the follower I saw two things I thought could be improved... the pebbled grain of the surface of the follower was a bit aggressive, so I smoothed it. Then, there was obvious excessive molding flash on the contact surfaces of it. I also smoothed the feed lips a tiny bit. I wouldn't my life on a ProMag Magazine.
Still going...
I bought three more to use for target practice and have not had a single magazine related failure in somewhere around 500 rounds total. Not a phenomenal number of rounds, by any means, but still representative of what might could be expected over time.
Not for everyone...
The point here is that out of the box, ProMag magazines are very hit and miss... in my opinion, some designs are only miss... but IF you don't mind a bit of tinkering, and have the knowledge and equipment, then ProMag may be right for you. If you are purely a shooter and don't work with your firearms or this is about personal defense, then its probably best to stay with quality factory equipment.
So some ProMag products might have their place, in my experience, and opinion.
MrBlackCat