First thing's first––-who really needs a 75 round drum magazine?!?! Anyone who wants to have a lot fun, that's who!
I picked these top loaders up from Apex about a month ago and the one in the video below was the one in the 'worst' condition but as you can see it's still in great shape for a surplus mag. There's a lot of controversy out on the forums about whether these are of Romanian or of Russian origin; I'll leave that to the magazine experts. I know they were issued to Romanian RPK gunners.... Other than that all I know is that they work well and there's lots of fun.
-100% reliable in 4 rifles I've tried them in so far
-Heavy (helps absorb recoil)
-Mil spec quality construction
-Relatively inexpensive now (I got mine for $79, but over the years they've been over $120)
-Great design; much easier to load than the wind up mags
-Heavy (can be a pro or con depending on intended use)
-Tough to load after 40 or 50 rounds
Here's a video of me shooting a couple rounds through my Draco and then I break them down and cover some of the pros and cons.