Which 4 stage RO unit to choose?

I thought about getting this one.. What made up my mind, with the other I can immediately tell when the DI resin is spent because I can see into the container because it is clear.

Not to steal the threat, but how do you know when the DI resin is spent. Mine is currently a tannish sort of color with green mixing in. Is the green spent resin?
 
The color changing DI resin I have starts out a dark blue-green and turns tan-orange as it's spent.
 
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