I really don't get what has led you to believe that M&M is any different in their advertising from other FFP's (I don't even feel they do advertise except in the flight magazines).
For me it sounds incredibly stupid to just assume that any fare class will earn you a lot of miles. It's quite transparant on the M&M site how many miles you will earn with each participating airline. Expecting deeply discounted fares to earn you as much as the higher ones is not very realistic. And as with all FFP's the miles for a single flight won't get you anything... That's just what people would like to believe.
The only thing I feel that M&M should be more transparant about is the fees/taxes they charge on awards. That's a practice that should be forbidden. But they are hardly unique and information about this can easily be found.
So yes, I still feel you should do your homework before joining. Being ignorant and assuming things is allways a bad idea.
What is in your opinion so wrong with what they advertise and what is offered?