I am replacing a shower valve with the Delta universal valve body. The current shower when turned on full hot takes around 2 minutes for the hot water to make it to the shower. So, I usually turn the current valve to full hot, putts around till the hot is full in the shower and then regulate back to normal temperature when I get in. My concern with the separate temperature knob is that if I leave it at the normal setting for showering it is going to take longer to get the hot water up and use more water while waiting. So, I am leaning to not buying the separate temperature knob, and just get the on/off knob and do as I do now to get the water up to temperature. I like the concept of a separate knob, but is it worth it really?