I run an EV180, and it works great, but ... it can be very sensitive to the outlet backpressure. If you let the outlet simply dump into a sump from above, then this won't be a problem, but I have a section of 1" tubing on the outlet that I use to run the outlet water down to the sump, just above the water level. It's hard to explain the layout but the skimmer sits ontop of the sump, and I imagine similar issues would crop up with the skimmer almost anywhere.
What this means (getting to the point) is that even slight changes in the sump water level, such as what happens when the sump pump is turned off for maintenance and water changes, the outlet tube is now under water and hence subject to more back pressure. This causes a slow rise of the water level in the skimmer - kind of a 'duh' for some readers, sorry - and this water can spurt out the air inlet valve (the 3/8" John Guest fitting or whatever your version might have), destroy the existing foam column, and rise the water level up into the collection cup and out through the not-water tight flange gasket, taking any collected skimmate with it, into the sump or onto the floor.
The same thing can happen when you adjust the gate valve on the outlet. It takes a few minutes for the water level to settle after doing this, so if you crank the valve back too much, not much will happen immediately, and if you leave the room for a minute, you might come back to water everywhere if the skimmer level rises as above.
I'm not sure this is really a design issue but maybe the nature of all skimmer beasts, being an open, pressurized system.
Another good point about AquaC skimmers is that they are built very strong, and the designs are simple but precise and refined. The only maintenance they seem to need is the usual cup emptying, wiping down the inside of the riser tower sometimes, and the same pump maintenance all skimmers need (cleaning, replacing o rings and impellors from time to time.) The 'spray injector' can be unscrewed and cleaned if it ever gets clogged, but the larger EVs don't seem to have this as a problem.
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