If you use a combination valve with a two way diverter, it will accomplish the usage pattern you want as long as the diverter has A, or B, or "A and B" options. BUT, the flow pressure may change because most of those valves have a limited capacity. A thermostatic only valve, such as Grohe or Hansgrohe, will have the capacity, but then you need separate volume controls. One advantage of this is that you only have to use one, (or two for both devices), valve to turn on the water. You do not have to turn on the faucet and then turn the diverter to the usage you desire.