I tried one once - it was interesting. The hair is synthetic, but grips more or less like normal hair and never breaks or needs replacing (major help) - but the sound is not the same as a wooden bow. The feel is also much lighter, which makes it great for fast passage work, but hard to play things like slow airs with much feeling. The bow is cambered like a baroque bow.
I didn't end up buying it because I prefer my normal bows even for fiddling, but they are certainly an interesting object and for the low price (only just over a hundred quid I think) - worth getting just as a curiosity!
Some people have recommended them as being better for fiddling that a normal bow - I think that's highly unlikely, a good folk fiddler has good violin technique and so uses a normal bow and most usually a normal bow hold (none of this higher up the stick nonsense - that just reduces the amount of bow you can use!) - but I do know a few fiddlers who have bought them once they were able to use a normal bow too.
Get one - you know you want to!
Allan