I haven't seen any complaints around the 'net that stand out to me about The ITM Mg Stem. There might be some but I haven't noticed anything bad about that model.
All I can say is the regular Millenium stem has given me no trouble at all. I've owned a few different sizes of it on a few bikes since early '00. It's become my 'go to' stem over other designs I've had (Cinelli, Deda, Ritchey, TTT).
It's very light (as light as I want to go in a stem for my weight), stiff, generally doesn't work its bolts loose, treats steer tubes and bars kindly - even carbon, and has a great looking finish. That's enough for me.
I'm using a 120mm Millenium now that's doing a great job. The ONLY complaint I have is there are times I've wanted a different angle than the 80 deg.