I think my tap water usually is around 200 TDS give or take.
So that seems to agree with that report.
The quality of the system doesn't really matter too much as long as you have a physical filter to remove non-dissolved solids and enough carbon to remove chlorine which will destroy a RO membrane. Then just get a gallons per day system that will work for you.
I replace my filters about every year (but then I've moved a lot) and I've replaced the membrane once after two years but that was my fault.
The only real trick is your RO unit should be sized with a flow restrictor that is rated for the output of the membrane. So once you go with a certain flow-rate module, stick with that one. Then the water coming out of the RO unit goes into the DI module and comes out TDS free. If you have TDS in the water out of the DI, it's time to change the DI. If enough people have RO/DI units that's something we can go in on a group buy - replacement DI resin.
I see systems now that come for drinking water that 'polish' the water after the DI with an additional carbon. I think that's silly unless it's going into a storage tank before coming out of the faucet.
I just have my RO/DI in a rubbermaid bin outside and hook it up to a hose connection. Then I run the brine into plants and another storage for gardening for a while, and then once full, let the rest of the brine flow out onto the lawn.
I ended up getting one of those dual TDS meters: one for the output of the RO and one for the output of the DI but you can set it up however. I also have a bypass on the restrictor so I can 'flush' the membrane upon startup/shutdown/ and every few hours of operation. I've been told this helps increase efficency and life of the membrane. You should also know that when it's colder the RO membrane doesn't work as well as it does when it's warm so you'll have a lot more brine.
Wow so they actually sell RO/DI units based upon TDS inlet? I suspect you might be looking at flowrate capacities. But this surely one be the first time I've been wrong.
If you end up paying more than $150ish you're probably looking too deep unless you want something that will serve your family's drinking water needs as well. (ironic, my aquarium has better water than I provide for myself.)