I lived on a small sailboat for several years and used these 
things every day -they are great. These days we use one with the 
Syncro Westie, leaving the unit up in the luggage area while it warms 
up.

The come in three sizes, one say about 1.5 gallons, one say 3 gallons,
and a jumbo that is maybe 5 gallons. We have  the intermediate model, 
and it is good for two showers, though you can't just let the spigot run 
free, you have to exercise serious water managment.

They do get hot, in fact, in some climes, too hot if you let them
sit in the sun all day. If its cloudy, or you are impatient, or its
just kinda cool out, the plastic bag is pretty rugged and you can
heat some water in your teakettle and pour some into the bag for a
heat boost. Other people with the largest size bags told me they take
a long time to reach temperature, which makes sense with the increased
mass.

The $19 price tag is about right for the large unit, but if you shop 
around you can get the medium one for about $13.

Privacy curtain? What, are you ashamed ;-)? Most of the time  we are 
someplace where it did not matter, or we didn't care  :-0 !  In close 
and public quarters, you can wear bathing suits, and reach inside
to do what needs to be done. Never felt the need for a curtain.
If you do, at $19- check the price of a shower curtain liner at 
Wal-Mart? 

Stay clean!

Tom F.