I was thinking the same thing a few months ago. Based on my spend patterns and usage, M4B is not worth it. Reasons is high fees and laundry list of exclusions. It would make sense only if I use it for everything instead of Infinia but then my net reward rate goes down.
I ended up getting Atlas. Now use Infinia and Atlas as combo. Any retail(in store) purchase goes on Atlas, exclusions on Infinia.