For all the faults with the PMUs, I think the grumblings over them are kind of overblown. Would I like them to be useable for any fare? Yes. Would I like there to be better availability? Sure. But, at the end of the day, I just don't get all of the people that complain about them. It is still more than you get from CO, and they still have their uses, even if not for everyone.

And, for all the complaints, my experience is that upgrade availability (which is the Z bucket for International tickets) is at least as good as mileage upgrade availability with CO. And, while I don't encourage anyone to buy a higher fare without the certainty of an upgrade, if an upgrade is available, I don't think your net cost of an M fare is going to be much higher, if at all, than a lower bucket CO fare + surcharge.

To the OP, welcome to the dark side.