The difference in price of the TF100 salt and TFpro salt is the nicer case and smart stir. You will absolutely want the smart stir either way.
But lemme tell you about the nicer case. Having had both I appreciated the organization of the TFpro *every last time* I used it. The TF100 was entirely functional and an even swap for supplies, but hunting and picking for that one bottle that always seemed to be hiding under something was frustrating. It didn't matter which test I was looking to do, the one I needed was winning peek-a-boo.
Having the stirrer with its own slot in the case is real nice too. I test right from the case and never had to move 3 things out of the way so it fit going back. And at that point, I had NO problems finding bottles in the way. Then I'd move them so the smart stir fit, and then need to find homes for those bottles, which would haunt me next time.