Some guys swear by it, but use at your own risk. Its something that has to be done properly or you will end up fucking yourself, and you cant go back in time to fix it.
Some pro's use it and you can barely tell, like Chris Dim for instance, but these guys are most likely having someone do it for them. Also, the biggest draw back to synthol is that you will probably show no striations where you inject making it very obvious you are using the crap.