I would be carefull with the NURCE system.
The way Nurce works is based on a siphon/vacuum - meaning when the water in your sump goes down, the water for the refill hose gets pulled through and levels it off -
The problem with this is that the fresh water is in constant contact with the salt water - now, you all know about salt creep, right, well, this is the same thing - the ionic transfer of salt to fresh continues to happen - this will eventually (albeit slowly) decreae your overall salinity, and then increase it again as the water tops off and evaporates - I know what you are saying . . . well, the float switch system does the same thing, right - well yes, but the float switch usually puts in like a quart or so, perhaps 2 - since the Nurce's are ually a few gallons large, this can dramatically effect your salinity and have it in a constant state of flux -
I have a friend who has one (I think it's 8 gallons) and he has had few problems with it - nothing major, but it lost its siphon a couple of times -
I would post an additional string to RC to see what some others have to say about it -
Just my $.02
House