Hey Nikki,
I have been successfully using the Petco Nutri-Sea water for over a year now. I have a six gallon reef stocked as can be, and everything is flourishing. I have had NO problems with this water, and all the parameters have been good for me right out of the box.
It did not make financial sense for me to buy a RO/DI unit when I am only doing a 1.25 gallon water change a week. My SI buddies supplied me with RO/DI top off water, and a gallon lasted me a month.
Once I upgrade, I will be purchasing an RO/DI unit and making my own water, but for now, this suits my needs perfectly.