Personally, on magazines like those in a Glock, the manufacturer original is best in many cases. I shy away from replacements like Mec-Gar and such. They may operate “just as well” but I don’t have to take that chance.
CDNN often advertises Glock magaqzines as “Asian Military”. They are probably OK but I would rather have Glock.
As far as Mec-Gar goes, they are among the best and in fact make most name brand magazines for them. They just put their name on them.
Mec Gar mags are GTG and are supplied as OEM mags by many manufacturers.
Mec-Gar in particular often IS the manufacturer original - many firearm makers contract magazine manufacture out to them.