Got one of them recently. Took it to the range once so far. I have 2 of the 50 round drums with it. The feed ramp in the drums is different on the 2. One feeds just fine. The other is a jam-o-matic. Judging by the makeup of the feed area, I'm going to have to do a little JB weld and dremel work, but I think it's doable. I originally bought it to thread the end for a suppressor (how can you argue with 50 rounds suppressed without reloading?). The only thing is, the barrel shroud on it is actually the same piece of metal that makes up the receiver. I haven't bothered figuring out how to remove the barrel, but if/when I do, it will have to be extended to be threaded.
As far as the fun factor goes, when using the drum that feeds 100%, it's a blast. If you are looking into one, I can take some pics of the different feed areas of the drums so you can check the one you are looking into.
And if you have a lead on a 30 round stick, let me know. I'd like to have one to go along with the drums.
Woody