My pool supply store where I buy my chemicals does a free water test that includes a tds count. I am more concerned with an exact ph count which my Taylor kit does MUCH better than the test strips, but i do glance at the tds count when i get the printout.
I am not saying it's true, but the tech at the store said tds is something that is much more important in pools than spas. His reasoning is that a spa is normally drained every 3 months so there isn't a big opportunity for this to make a big difference. I would love to hear others opinions on this, although I don't plan on adding tds on my list of things to stress over at this point.