I only know from experience, not from any intellectual research. I'll take an educated guess though.
The cheap $100 RO units just have a really weak pump I think, which is why they give low GPH. If you want something that gives high output, you need a good pump FORCING the water through the filter media. There is a lot of resistance as it gets filtered.
I work in a biology research lab, which is why I know some about these. Thermo is a equipment supplier for biotech. So, their unit can't just slowely drip water out like the 100 dollar ones a lot of reefers use. It has to be able to fill up bottles to use for reagents, media, etc. So, no one would buy these if they flow rate was slow. Not sure on the price of that unit he listed, but if I had to take a guess I'd say 1-2k dollars. On all the lab grade filters, there is a high flow rate, as well as a gauge to measure resistance across the water. Once it drops from 18 ohms, its time to start thinking about replacing filters.
I have a pretty large size filter in my basement that I got from a lab that was getting taken down. Think probably weights 50 lbs, but it can fill a 35 gallon garbage can in about 100 minutes. The one I have is usually installed under the sink and would have its own 'DI water faucet' attached to it.
As for waste water, I've really only used lab ones. I'd guess you run if for a minute or 2 to get the resistance up to 18 ohms, and maybe that would be 0.5-1 gallon of water, or thereabouts.
Again, I just have experience from using these. I don't really know much at all about the filter media, etc. I had one set of replacement filters on mine, but when I have to do it again, I'm probably going to have to talk to the guys at filtermidia.com or something to figure out what to do, as my millipore filter is made in germany and is all metric. I'm hoping I can find some cheap aquarium grade filter media to put in, as I think ordering the actual replacement cylenders from germany might cost some crazy amount of money, but I haven't looked into it yet.
