units are all basically the same, there is no "special" equipment that Kent has over the others so your paying for the name.
The last time I did a search on this there were only 2 companies that make membranes "the heart of the system" and they are both good membranes.
So the only real difference is the other filters, Micron filters are nothing fancy.. Carbon, there can be a difference in the quality of the carbon, but IMO
not a real big issue if you stay on top of changing them out.
resin here is where there can be a bigger difference, but when its time for new resin just get a better resin.
There are bells and whistles that some units have over the others.... IMO
the ebay units are good units.
The only thing I don't like about some of them are the ones that have the DI
laying on top of the unit, when its like this "channeling " of the resin can happen and you will not be getting the most out of the resin this way.
The units that have a housing just for a resin cartridge are better IMO
Also a 75 GPD unit is the most efficient unit out there, so unless you need a ton of water fast a 75 GPD is all you will need. Having used a 75 and 100 GPD membranes there is not much difference in water output..