Sounds like you want the Purist based on how it operates and how it looks but you want the Grohe based on price. Only you know your budget, but I'd go with the Purist. What? Every day you're going to take your shower and kick yourself for getting the model you didn't like? If you keep it a decade, that's 15 bucks a year. Twenty years and it's 7.50 a year.

Yes DreamingoftheUP I do like Purist! But is a Grohe better in the long run?

I don't know which is better quality. Just thought I'd chime in on the proc/cons of having both showerheads on at the same time. My valve from Hudson Reed lets me do that, and I've only used it for that purpose, perhaps 2X in four years. I have a 3/4" line coming to my shower (so much bigger than the normal 1/2" line), and when I have both on full blast, I run out of hot water pretty fast. So I basically only have one or the other on anyways.

For me, what is really really convenient, and I would never choose anything else, is being able to have the temperature pre-set and being able to have a volume control. Some valves are only off/on, no volume control, so be sure to check that.

Personally, I have dual function being shower head and handshower. Mine the handshower lifts from the middle of the head. Both of use this every day, great feature and would not go without it now that we have one.