If you want to get a controller, i use the digiq dx2 and it works very well on my WSM. I bought the bbq guru stainless 3/4" ball valve adapter for my uds but i never use it.
With the uds I find it is more important to pay attention on how you load and light your charcoal. I have 3 - 3/4" pipe nipples on mine and basically run one wide open, one closed, and adjust temperature with the ball valve. Catch your temperatures on the way up and start closing down when you are 25-50 degrees from your target temp. I find that once I have the uds set, it chugs along within 5-10 degrees depending on how windy it is outside.
I would say try doing it manually - it won't cost you anything but a little of your time. Try to learn fire control - it is much easier than you think. If you are concerned with the what ifs in the middle of the night, buy a maverick 732 or igrill which have user programmable temp alarms and will alert you if your temps fall outside of your target range. If you find that you don't like doing it manually, then spend the money on a controller.