If you want to save water then yes, definetly get a controller, get yourself the gardiners liquid logic controller, I have got 2, and they are 2.5 years old and have never had a problem, once the calibration is set properly you will it have a problem.
The varistream controller seems to have problem from what I have read and do not seem as reliable, I could be wrong though.
Some people have problems with digital controllers because they do not set them up properly, or there is a problem with dirty connections.