At 028 tds you could clean windows with that alone. But i wouldnt chance it, tho many have and do as its well under the mark of what the human eye could see.
However to answer your question i would have thought it boils down to cost. As in, how much do you spend on di resin per month, how often do you work (need to produce 000 water) and would you have a static tank for storage. Im sure an ro systen would take it down to lesss than 010 and again cut out need for regular suply of resin. So then its the cost of which RO compared to Di and cost of water if on a meter (for waste to pure ratio)