Floyd R Turbo
Either busy or sleeping
...or the extra benefit over a traditional fuge.
I can address this one. At worst, an ATS is superior to a refugium (growing algae for the purposes of nutrient export) because
1) you can position the light source much closer. Light intensity is a function of the inverse square of the distance. If you are 2x as far away, your light drops off by a factor of 4.
2) In a fuge, light cannot easily penetrate through to the deeper layers due to the growth nearest the light source blocking the light (needing to rotate a ball of chaeto comes to mind)
3) you can achieve much higher flow rate over a larger area, namely at the boundary layer where the actual nutrient exchange happens. This is why a thin sheet of fast moving water across a vertical screen works better than a pool of moving water, unless it's moving really, really fast all around.
4) you have to periodically trim whatever is growing in the fuge. You have to periodically remove the algae from the screen. Not much different here.
5) there are types of macro in refugia that can 'go sexual', and from what I remember, this can cause some serious problems. I have yet to hear of anyone having their algae scrubber algae 'go sexual'.
Those are the main ones off the top of my head. When I first started looking at the ATS, I was going to do a refugium for the purposes of nutrient export, mainly phosphate, which kept climbing up no matter what I did. I came to the conclusion that at its most basic form, an algae scrubber is indeed a super-concentrated refugium. If you consider nothing else but the items above, I have a hard time seeing how you could not arrive at this conclusion. There are many examples where people have run an algae scrubber and their refugium gets out-competed by it quickly.
I hope that's at least one thing I can say about an algae scrubber that won't get criticized as not presenting indisputable scientific evidence. I just can't understand how you could be pro-refugium and against the algae scrubber, because like I said, that's what it is at it's core.
Disadvantages? The main one I can think of is the extended power outage. But you would need one more than 6 hours to really start to do any damage to the algae, while macro in a refugium would likely be OK. By this time, you'll start losing fish and coral in any system, so you'd have bigger problems no matter what. If it lasted longer than 6 hours and you weren't there, when the power kicked on you could start to get algae detaching from the screen and getting back into the system, but for the entire screen to die off and require a start from zero it would need to really, really dry out, and you would have a tank full of dead fish and corals by then, unless you had a battery powered air pump that lasted a very long time.