As they are small, these devices are very mobile.  You can easily take them to the cottage or camping.  Some units now have electric bases so that you don't even need the stove; just plug them in anywhere that there is an electrical outlet.

When choosing between models, they are differentiated mainly between aluminum and stainless steel materials and a variety of sizes and aesthetics.  They are measured by cups but this refers to espresso demitasse cups, which are only about 1.5oz each cup.  They can range from about one cup up to about 18 cups.

Note that with these units, there is a gasket that will need to be changed approximately every six to nine months, depending on use (not expensive - approximately $3 - $4 per gasket).  Make sure that you know where to get the correct gaskets for your unit as they are not usually interchangeable between brands.  Different models have different shapes internally and the gasket needs to be perfect in order to ensure a good seal and work properly.