At this point, I have officially joined the "anti-airlock" brigade...
I started using a blow-off tube, and have had nothing but good luck.
One thing I have noticed is that at high krausen, the foam is a nice thick rich dense mat, compared to my "airlock" days, when it would be lighter, airier bubbles that would fill the entire head space of a 6.5 gallon primary. I have looked at video after video on Youtube, and see the same thing over and over again. 6.5 gallon primaries with a blow off tube have a nice thick rich mat of yeast/foam, about 1-2 inches, those with airlocks are full to the top with loose airy foam.
One advantage to this is that it makes cleaning the carboy a whole lot easier. Another advantage is that you don't have to worry about cleaning the blow-off tube, if the foam never comes close to reaching it anyway. In looking at videos, there are tons where the airlock if full of foam, foam shooting out the top, etc. Then you are cleaning the airlock, the counter, the floor. You are pissed, your wife/girlfriend/roommate is pissed, the dog is pissed because he has this bitter sticky sh!t on his paws, and he does not want to lick it off... it just isn't a good thing. I have only seen one video of a nasty looking blow off tube, and the dude was fermenting in what looked to be a 5 gallon secondary. DUDE... if you are on here, what the hell were you thinking?!?!?!
Now, here is my theory on why this happens. When you use a blow-off tube, you are giving the co2 a way out of the fermenter that is as unrestricted as possible. I use 1" id tubing, about 6 feet of it, running into a bucket with 5 gallons of sanitizing solution that is left over from that days brew cleaning. With no major restrictions on the escaping gas, the pressure in the head space should be less than the pressure inside the bubbles, and the bubbles should break quickly and easily. When you use an airlock, you put some serious restrictions on how fast that gas can escape. This would result in at least some pressurization of the head space, and my thought is that this makes it easier for the bubbles to stay formed for a longer time, since the pressure inside the bubble is not any greater than the pressure outside the bubble.
Take this all with a grain of salt, as I am just a noob with only 7 batches under my belt, and only two of those were with the blow-off tube. There may be a ton of people out there who use 6.5 gallon primaries and large diameter blow-off tubes, and still have problems with too much foam, I am simply basing my comments on my own observations, and on what I have found while searching videos online.
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