Great that you love AA, I do too
. Distilled water is pretty much RO water. Deionized water is not safe to drink. So it will have more TDS whereas RODI has or should have 0. The TDS can feed hair algae. If you can afford it, I'd highly recommend getting one. Doubt you want to be lugging 40 gallons to make the water from the store to your house, then 5 gallons or so every week for water changes. Plus you know exactly what's in going into your aquarium..pure water and nothing else! One thing though is that for every gallon of RODI water made, there is 4 gallons of waste water. You can hook it up to your washing machine or lawn to save water and money. That Petsmart water is prob. just RO water and what's with that "magical bacteria"? I bet it's a lot more expensive b/c it's "special water for aquariums".
They don't even sell SW fish (just saying).