I'd stay away from it.
I'm assuming this is used.....and therefore you have no idea of the condition of the membrane or filters. In addition, the filter holders appear to be very thin, so it doesn't take conventional filters. Also, the holding tank is for a water system on a sink or icemaker....you don't want to use that for making water for your tank. And finally, you'll still need to purchase a DI filter to get 0 TDS water. By the time you purchase all the new membrane, filters and DI unit, you could have purchase a refurbished Spectrapure.