I have one of the loaders. They are nice for the 25 rounders when you just want to spray lead down range, and I haven't had any problems with mine jamming.
What I HAVE had problems with however is it not quite seating the cartridges all the way back in the magazine, and I have also noticed that it tends to dent the bullets. Probably not the best for accuracy, and I have noticed more feeding issues after using the tool, than when I load them by hand (no ftfs/ftes when I hand-load my mags).
Funny, after buying the 25 rounder mags, and the loader, I still prefer handloading the factory 10 rounders. Those magazines are great. Which reminds me, the loader will load factory mags as well, not just the hot/steel lips mags, just in case you were wondering. It's not clear on the package that it does.