Mec-Gar mags ARE every bit as well made and reliable as factory magazines.
I have used Mec-Gar magazines in my Model 59, My Model 659, and now in my Model 5906.
I also also used Mec-Gar magazines in a 9mm Sig, a 45ACP Sig, Beretta 92, and a FN Hi-Power.
I've never had any problems of any kind with a Mec-Gar magazine.
The spring in one of my 17 round S&W Mec-Gar did get a bit weak, after many years of use at the range. Meg-Gar sent me a new spring, at no charge, when I called them up to ask about buying a replacement spring.
They have a lifetime warranty, and they even warranty the spring.
You can't ask for much more than that.