I have the one you are looking at on ebay and it's very well made. I've seen a lot of disucussions about GE Desal membranes vs. Filmtec with people usually saying there is no comparison to Filmtec, but a couple people posted TDS results from the exact model you are looking at, the 100gpd, and the rejection rate after the RO, before the DI was about 98%, so I guess the GE Desal membrane works fine.
Another reason I like this unit is the dual DI. Someday I may try to get some some separate anion and kation media for the separate cartridges and be able to recharge them instead of discard once they're spent.