I have two, a round one that you can roll on its stand to mix up the material, and a rectangular one with no bottom
the tumbler one works faster, although it also gets more sun and heat might play a factor. I moved the other one next to it today
the other one works too though it's just more of a pain to mix teh stuff up. When I moved it there was a ton of compost at the bottom, but unfortunately it was also a huge web of fine roots. It was on the edge of my property line next to an oak tree and some brushy stuff. Finding the root mess today was another reason I moved it
I usually mulch my grass with my mower but a couple times a year, especially if I find the composter is dry and mainly browns, I'll put the bag on it and put the grass clippings in. I also put some of the fall leaves in them. I also do vegetable waste from food, occasional stale or moldy bread, and coffee grounds. I don't put meat or fat scraps in though as I've heard that will attract rats, coons, opossums, etc