I had a NatureMill for a couple of years. During that time, it tended to smell, jam, and the glue in the seams cracked. Part of this was my fault as I put a lot of "green" matter into it; part of it is just problems with the NatureMill. First, what the instructions tell you is "green" or "brown" waste is actually inaccurate- for the longest time, I couldn't figure out why my compost was wet and smelly, when I was using both kinds of material. When I finally got a plain-Jane composter, put it on my deck, and read the accompanying guide about composting, I realized that what I had thought was "brown" material because of the NatureMill cheat sheet actually isn't. Basically, you need wet [green] material and dry [brown] material, and some of what NatureMill says is brown is actually green. The NatureMill seems to need a lot of extra "brown" material in order to produce compost- my traditional composter doesn't suffer the same problems as the NatureMill did, despite my eating and composting habits being the same now as then. I now get sweet-smelling, rich, black compost that makes my plants gorgeous and takes no effort on my part. I just dump the scraps into it, roll it on its base, and get great compost.
I really wanted to like the NatureMill, but it just didn't work for me. (They also didn't honor the warranty when the sides split apart due to the glue failure, but that's beside the point.) For me, the NatureMill is a lot better in theory than in practice. Once in a blue moon I would get brown, crumbly compost from the NatureMill that looked a lot like shredded bark, but more often than not, I got nothing useful. The capacity is also quite small on these. If you eat a lot of vegetables and try to compost the scraps in a NatureMill, you might find that you need several of the mills to keep up, and you're going to need a lot of sawdust pellets if you eat a lot of vegetables.
For about a hundred bucks, I got a much better composter for my deck. If you can ONLY compost inside, then you might want to consider a NatureMill (or several). If you have any kind of outside space whatsoever, however, you're probably better off with a countertop canister inside and a traditional composter outside. In that respect, picking up one of the countertop compost collectors here might be worth doing. Note, however, that you will never get compost from one of the countertop units alone- they're just meant to collect your scraps so that you don't have to run out to the actual composter all the time.