I use a blowoff tube, but only to stop my airlocks clogging. We use 19 (and a bit) litre watercooler bottles as fermenters, so there's not much headspace when you have 17-18 litres of beer in it. The tube blows off loads of yeast, so we end up with a cm or more layer of it in the blow off vessel (filled with sani), but it doesn't take away the gunk really as this still gets plastered to the sides of the fermenter.
So in my experience it's worth it if you'd normally use an airlock and don't want to risk it getting bunged up. In fact, a mate in work just had his wife on the phone telling him a bung with an airlock just flew off a demijohn at home due to the krausen clogging it <!-- s:D --><img src="{SMILIES_PATH}/icon_biggrin.gif" alt="

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If you use a bucket/brewbin, it might help direct aggressive krausen out in a controlled way so it doesn't seep all over the place.
It also look cool <!-- s;) --><img src="{SMILIES_PATH}/icon_wink.gif" alt="

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