Are they any good, generally?
If so, is a cheap one like this
http://www.taps4less.com/PP/U-CD324.html likely to work as well (or
almost as well) as the many much more expensive models out there?
That looks like a wax pellet type, which is OK if the incoming
water pressure and temperature aren't likely to change suddenly.
If you're going over to France, it might be worth looking over
there. The shower-only version of this are about 1/3rd of the
price over there that they are here.
These don't work very well with instant water heaters (combi
or multipoint), where for the shower, you really need a fast
acting mixer which can also cope with mismatched/varying
pressure, but that's significantly more expensive, needless to
say.
Note this particular one needs 1 bar pressure (i.e. the tank
needs to be 33 feet above the tap, if it's tank-fed and not
pumped). There are taps which can operate at 0.3 bar (10 foot
head), although I don't know about thermostatic ones, and the
shower wouldn't be up to much at 0.3 bar anyway.
