Unless I've misread the thread, the chap has subsequently written off the car. On that basis I'd have to say that those who think this is acceptable because in the clip "he seemed to be incontrol" are wrong. Drifting is intentionally pushing a car beyond the limits of its adhesion and you're treading a fine line when trying to maintain control. It sounds like this chap is not as skillful as he thinks and the thought of a 1.5 tonne car out of control should be enough to convince anyone that this sort of behaviour on a public road is a bad idea.
I'm sorry to hear about your experience and hope that it all gets sorted soon. It is important that feedback on traders is posted whether good or bad as, if we only posted up the good, people might get a false impression. Good luck with it.
The BM's are ruthlessly efficient at what they do and that diesel engine is a gem but they lack the character and passion the Zed has in spades. If you're getting bored of the Zed now, I'll give you 3 months in a 335d!