I have run them in 6 different STI/Staccato pistols and 2 Prodigy pistols. So far I am right at 1,000 trouble free rounds thru them.
Right off the bat I noticed that when loading them they seem to keep the rounds "tighter" in the mag tube. When I get to about 6 or 7 rounds in the factory Prodigy mags I can shake the mag and you feel and hear the rounds moving back and forth. I have had rounds nose down in the Prodigy mags due to this. Not so in Mec-Gar mags, they seem to hold them tighter.
For background, I have 50+ "old" style 9mm STI mags and 40+ Staccato latest gen 9mm mags and 28 Prodigy mags.
Going to keep running them (and ordering more) and will update if I start having any issues.