Yes, lots of people use the vending machines for their tanks. I would however invest in a $20-25 TDS meter to make sure you are getting clean water. Its not uncommon for these to not be maintained the way they should, so as the filter material breaks down, you go from low TDS to high TDS between fill ups. You just want to test and make sure the water coming out is still good each time you go.
That said, in the long term purchasing your own RO or RODI filter makes a lot of sense. A system that can produce 50 gallons a day of pure filtered water will only run you $100-130. If you don't want to mess with plumbing, just get a unit that screws into your kitchen sink faucet when you want to use it. If you are only using it for a couple tanks, the filter materials will last a year or more between replacements.
It will quickly pay for itself vs the cost of purchasing water and lugging it home.