Despite it's drawbacks, mentioned above, I find that I really like my 3rd gen R100 sump. It's been in place for over 6 months now...
I'm actually using the built in float valve. Works fine. There is little play between full to the marked water level, and sucking air into my pump, even with a 90 on the pump intake facing it down. Using a Eheim 4000l pump. As long as the ATO reservoir isn't empty, it's fine. If I let the reservoir go empty, it's sucking air in a day. No big deal, I suppose... and it let's me know that it's time to refill the ATO.
Pulled the sock and tossed it... never liked 'em. I cut a length of 3" PVC to hang in the opening, just to quiet the splash.
I drilled the 5g Eshops ATO Reservoir and mounted a float valve near the top, plumbed it direct to my RO/DI, with an in-line valve. When the reservoir is low, I open the valve, and let it fill. The float valve keeps it from overflowing, should I forget to turn the valve off right away. Not a perfect solution, but it's fairly safe. Oh, I do have a water alarm under the ATO reservoir, and another at the rear corner of the sump. Just cheap battery powered alarms I picked up on amazon.
Reef Octopus SRO1000sss skimmer. No macro algae in the refugeum section, I use it for the original purpose of a fuge... a refuge for copepods, gammarus and mysid shrimp, worms, other critters to reproduce without pressure from the predators in the main tank. Working out pretty well for that.
I'll eventually be adding a GFO/GAC reactor, probably one of the cheap ones that BRS is selling. No rush, not enough critters in the tank to need it yet. Heck, I just added the skimmer last week.