In reply to Davinamo:
I bought a Silly Goat brush last year from Steve when I met him in a campsite near Font. We'd chatted quite a lot over the week we were there, he'd shown me his brushes but it was only on the last day I decided to buy one.
I do a bit of woodwork myself and there's no doubt that I'm a bit of a sucker for a well-made, nicely carved wooden thing anyway. It looks good and feels really nice in the hand. I'd also had a really good and enjoyable Font trip so was certainly in a feel-good mood when I bought it and the brush is something of a Font souvenir, a place that, while I'm not principally a boulder, I do have a lot of affection for.
So the reasons I bought the brush are no doubt mostly emotional. But it is a good brush with dense, stiff bristles. Steve says that they are long lasting and he worked a lot with various brush manufacturers to make a design specifically for the purpose. I haven't really had mine long enough to judge its durability but it does a good job of cleaning holds.
There are three sizes - the one in the OP's link is large and probably more suited to walls than outside bouldering. I have the middle size - Jack the Lad - named after Steve's son (or was Steve's son named after the brush?). I got it from Steve for 25 euros.
Steve will replace the head and at least the first time is free - maybe more. I guess you'd pay for P&P.
To be honest, I wouldn't have bought it from a shop - I've just used tooth brushes before. But I have no regrets buying the brush, I like it very much. I can think of plenty of times I've got much worse value for money out of 25 euros.