I have never seen a fish exposed to Q avert their guts. Again, I use it in the lab to put fish to sleep, it does a great job, doesn't seem to have any side effects. Clove oil is similar but I would suggest it is harder on fish, at least the fish I have used it on. Tricane and 2-phenoxyethanol are also commonly used to put fish to sleep. Tricane is FDA approved for food fish. All of these drugs can be used safely, all of these drugs can and will kill fish.
I think the problem is the person using the drug. If you mix it too strong or with Acetone as some collectors do and use so much of it "knocks" the fish out then you would have problems. I would suggest that almost every jawfish collected in the US for sale is collected with Q, so are many eels and some other fish that live deep in the ledges. Nobody with any skill at all uses it to catch a large percentage of angels.
All this said, I think a study would need to be preformed using proper protocols to say if collection of fish with Q is bad for the fish. I am sure this would very from collector to collector. As posted in another post, nearly every collector in Florida uses it on some basis or has a permit for it. So I would look for the honest collectors that at least tell you which fish they are using it on and which ones they are not.
When it comes to using these drugs on fish, at least in the lab, it is harmless and even helpful in reducing the amount of stress a fish is under when you are moving them around, examining or treating. I am not suggesting that it should be acceptable to use it to collect fish, especially if someone is lying about using it, uses too much of it, mixes it with Acetone.