understanding multiple ro membrane use
 

So I've watched the brs video and it seems you run the waste line from membrane 1 into the input for membrane 2. The way I understand it (assuming a 4:1 waste to pure ratio) you reduce the volume of water by 20% or so (4 gallons waste from 5 inputted) so the tds in the water leaving membrane 1 should be 20% higher?

If I follow this right the outputted water from membrane 2 is going to be slightly higher tds. The end result of this dual membrane conversion would be less waste produced overall and a slight increase in the amount of di resin consumed?

Anyone here do this upgrade? Pros or cons? I'm aware of the pressure requirements...

TDS numbers will be generally unaffected. The multiple membrane use appears to be purely provide a reduction in waste water.