As a hydroponic grower also, I would urge you to reconsider your ideals on TDS and pH, both of these pieces of information are invaluable, and should be measured as often as possible. TDS and pH should first be measured when evaluating your water source for any: hydroponic, coco, aeroponic, or soil grow. In the best of circumstances a reverse osmosis system should be used to to get your PPM down to an acceptable baseline, but I have seen many water sources where it was not needed (without this measurement you are flying blind). Without getting your baseline PPMs at an acceptable measurement you will be robbing crops of valuable available nutrients before you even start. The advantage a PPM measurement gives during the growth cycle is a window into how effectively the plant is up-taking nutrients, and how much nutrient solution should be added to the system. Without this piece of information the grower is simply taking guesses on how much solution should be added to the reservoirs and may be inadvertently locking out nutrients.
PH is the other variable in this equation, as you well know pH is the driving factor for nutrient uptake into the root system. In order to determine how much acid is needed an initial measurement of the water source should be taken, and of course measurements as the pH is adjusted. For the systems I have built the electronic pH meters have been a great value. The value add the electronic meter brings is repeatability, with the advent of newer pH meters with less requirements for recalibration a constant stream of pH data is not only inexpensive and accurate, but imperative to optimizing and notifying when a problem arises. A hydroponic grow can turn south rather quickly if the pH of the system fall out of balance the sooner the problem can be identified the less stress on the plant. Creating a hydroponic system that just grows is not a hard task, but for the low cost of sensors there is no reason not to have an optimized hydroponic system.