I haven't had any problems either but I know using RO will make them even better. I already got the unit on the way so we will see. Heres my logic, when you use tap water with the salts and minerals that the plant doesn't need the osmotic pressure will be fighting the roots as far as uptake of nutes and such.

When you use RO there are a few things I think would happen

1. Toxic salt build up takes longer then plants are more stress free and they yield more.

2. Along the lines with the salts you can go longer without a res change if you really want to.

3 Nutrient uptake should increase efficiency, only nutes that need to go to the plant are there and the whole osmotic pressure deal.

If A= Initial RO purchase and extra water and B=Increased yield (Monetary value)
then if A < B its worth it...and from my experience and reading I would think that is so...plus its good drinking water.