I'm not a pro...I've put in several Grohe faucets and valves and have been happy with them. Some people here have said wait until you need parts. Hopefully that will be long after I move out. In Europe, Grohe is pretty big. KWC is maybe the biggest faucet company in the world. If you ever use a themperature controlled valve, you'll probably want one at home. I really like mine. The first time I ever used one was in a hotel in London, England. It responded quickly when the water pressure changed (which can happen alot in a hotel). All that gets adjusted is the volume control, even if you are near the end of the hot water in the tank. Course, it can't make hot water...but no adjusting to maintain the temperature as it is used up.
Grohe also makes a double showerhead called the Freehander (if I remembercorrectly). You can turn one of the heads off if you wish to save water. With a divertor, you can have any arrangement you want, tub filler, hand shower, wall mounted shower. Keep in mind that if you go over probably 2 shower heads (on at the same time), you may really want to consider 3/4" supply and valve. This can be a major endeavor if it is not there already. Is your water heater big enough to support the volume? An average showerhead is about 2.5 gpm (double-check this figure - my memory may not be correct). The most you'll get out of a "normal" 1/2" supply is probably 6-7 gpm (varies with pressure and distance). Some valves won't flow that much.