I use the api salt water master test kit . not because of price but because of ease of use. I have been thinking of getting a rodi system but I dislike the thought of waste water. I've never had a problem before with my tap water . I do have more than 60 pound of live rock and use purigen in my skimmer over flow to reduce nitrites and nitrates . Also all my fish are juveniles so the biggest i have is about 1.5 inches
Well, you get waste water for a reason after all. I'm new to the reefing part as well, but RODI water is one of the main things every succesfull tank incorporates. From all the threads and tips I've read on here it seems reefers have more success when transitioning from tap/treated tap to RODI.
In the end it's not even expensive to set up at home - I think I paid $60 for the RO/DI setup and hung it from strings in the shower so I can forget I left it on without getting water everywhere. Wastewater is straight down the drain.