I would never have bought the 90EX flash,
unlike others, I received mine without the flash. After a quick email to B&H (and some help from some users on this forum), I got the free flash. Not really happy with it (no bounce, inconsistent output, no controls,push-button power switch) but I can't complain. It was free. It's much more well balanced than having my 430 ex ii on top of the M.
I'm with neuro/private though. I would never have purchased this flash.