I have another one with a longer can and I can do two or three small bottles, just have to pack them very carefully. Yes, not being able to do the outside is one drawback, and don't think I haven't tried to figure out to do it with this setup. I do have some aluminum oxide, but haven't had much...
If you want something cheap and easy to build, try an old electric ice cream maker. It turns around 40 rpm and does a great job cleaning the inside of the bottle. I use cut copper, comet and water for regular stains. Soda ( sick stains ) will take more time and a little more abrasive. I put the...