With a few days experience, it is pretty easy to figure out how much alcohol fuel you need to boil a kettle of water.
The idea of adding a valve and fuel supply to a burner seems appealing but one of the main advantages of Trangia burners is that they never, ever fail. There is nothing to go wrong, break, replace. I managed to burn the rubber ring on the screw-down cap but the burner remained operational.
The simmer ring is brutally simple in design. It isn't the easiest thing to use and I generally adjust it with my leatherman pliers but once you get into the habit, it is OK. I can adjust mine in very fine increments.

The flame adjustment on a cat stove is...another cat stove. By adjusting pattern of holes that you punch, you can adjust the heat output.