IIRC when they first came out they had some issues, but everything I've seen recently seems to indicate they're much better now. As good as Magpul or Lancer? No, but getting closer. For a range mag I'd use them but for serious purposes I'd pass.
MFT holds my personal top slot for crappiest AR mag I've ever used.
Past 20 rounds the lips spread so far you could smack it and rounds would fly out. I gave mine away to a friend after we finished his PSA build and he didn't have any mags to test it with.
Take a fully loaded magazine put it in your rifle stand over concrete walk or floor drop the magazine free. If it loses rounds on impact I'd be looking for better magazines.
A friend of mine just did some abuse tests with his MFT MOD II mag and it held up, no rounds came out. I heard they fixed the quality issues with the MOD II.