I've got one with a Wheatly sten grip conversion. Works fine, and the mags are pretty reliable, in my experience. I've got a ton of sten mags and would occasionally find one that didn't run perfectly, so I'd just set that one aside and not use it anymore, but most of them ran well right out of the box. I also use them on my Oly pattern 9mm upper.
If you want to do caliber swaps, you'll prefer the GG grip or an Uzi grip, since you just can't fit 45 mags into the original or sten mag grips.