I too would recommend your friend joins yahoo feline-hyperT group. I joined for a while a few years ago when Tom was "borderline" hyperT. I found out quite a lot.
Main concern
at that time seemed to be the high doses initially prescribed by vets across the UK. I understand it is now recommended that doses start low and gradually increase to let the body get used to the medication. I just wonder if the doses may have been too high, hence bad reaction? Really just a thought, no more. Felimazole is easier to give in small doses than Vidalta. I've not heard of Bercazol and can't find it listed in NOAH.
Shoot me if ya like but I'm afraid I would be dead against trying homeopathy for such a very serious condition.
Am sending best possible vibes for your friend's cat and every sympathy for your friend