I have not compared reaction time for thermostatically controlled valves. But, my first experience with them was in a London hotel...it was obvious that the water pressure was fluctuating all over the place, but the valves they had installed were Grohe Thermostatically controlled ones and I never noticed a temperature change. I ended up putting one from them in my bathroom remodel. Now, it is entirely possible that they also incorporated a pressure balance valve in their design that would help prevent scalding, but from what I can tell in mine, it does not, and relies on the thermostatic properties of the control valve to handle the job.
