I was debating the very same choice, but decided to go with the MEST (thank you, Musicteck!). I'll be interested to hear your thoughts on the IER-M9, if you decide to share them.Thanks for the advice and comments regarding my debated purchase of the MEST. I've decided for now to go with the Sony IER-M9, I've wanted it for ages and concerned a time will come where it's no longer available, already becoming more difficult to find. The MEST or various iterations of it I've no doubt will still be here in a couple of months when I've the urge/saved up enough cash again...
As for the MEST? I'm still fiddling around with tips (neurotically reading all the reports about fit issues got into my head, I think), but these are still such a quantum leap over any gear I've head before, and I catch myself involuntarily smiling like an idiot when listening to them, so that's a good sign, right?