I'm doing it at the moment, it's damned hard, I somehow passed the first 3 written exams, but got a day of oral exams in September that I'm dreading. Compared to the RFS cert, it's much harder, and strongly geared towards the new BS5837 and legislation and guidance notes and APNs and all sorts of other things I should know more about. I think it's pretty hard and strongly geared for tree officer types to get formally recognised qualifications.
If anyone's got any tips for the on-site exams, they'd be much appreciated!