Rotating composters speed up the decomposition of kitchen and garden waste by distributing air and water and breaking up layers of material that have been compacted together. Of course, you can and should break up material in a traditional composter with a pitchfork or shovel, but rotating composters are easier on your back in most cases. Tumblers make the process easier by placing the bin on a stand and adding a turning crank.
Whenever the material in the composter is turned, the material inside starts to break up more quickly. Moisture and heat are kept in, and the contents are mixed well. Some compost bins for sale claim that the process of creating compost can go from taking a few months to taking a few weeks.
If your composting bin is outdoors, then there are other advantages to using a rotating composter over a fixed one. The fact that they remain closed, keeping the smells of the decomposing foods inside is a bonus, and as long as they are latched and on a stand, they're very hard for backyard animals like raccoons and opossums to get into.
Then again, if you're on a budget, or if you're composting a small enough amount of waste that you can easily upend your compost container or stir it with a garden fork, you may not find a tumbling composter to be that much of an improvement over a simple closed bin.
Whether you choose a fixed or rotating compost bins, metal or plastic compost bins, you're doing yourself and the earth a favor by diverting useful substances from the waste stream. You can compost most kitchen waste, except for meat, bones, or dairy products. You can compost crushed egg shells, used coffee grounds, and even small amounts of shredded paper. The result, after a few weeks or months of decomposition magic, is a crumbly, nearly black substance that can be added to soils to greatly improve them without the use of chemical fertilizers.
Even if you don't garden, you can add compost to the soils in house plants, or you could give them to a friend who gardens. Good compost is often referred to as "black gold" because of its many benefits to soils and gardens. If you do garden, mixing compost in with your normal garden soil enriches it and can improve garden yields with little extra effort or expense.
Adding compost around bedding plants and trees enriches the soils, discourages weeds, and even discourages some insect pests. The combination of ground up dead leaves and grass clippings makes terrific compost over the winter that you can use when you plant in the spring. Composting is one of the easiest, most earth-friendly practices you can undertake, and there are plenty of ready-made composting bins that will help you do it.