I have both, and I love them both. The key, I have found, is loading the Pietta 50-round drum like on that You-tube video, (it comes up 2dn or 3rd when you search "pps-50 drum mag" where you take the side cover off, preload the spring all the way around, and just drop the rounds in one at a time, nose first. In fact even with he "tool" I have been unable to load it any other way. But I have yet to have a SINGLE misfire whist loading it from the side like this...plus, it's FAST to load! I like the PPS-50 because it's a handy little carbine-sized unit. I put a swivel stud for a bipod on it. The bipod leg doubles are a makeshift foregrip, as well, like an old WW2 movie, lol...
I have a short video of 50 rounds through it without a hitch, if I can figure out this drop-box app. Trying to get it from my phone to Youtube...too big a file to email.