Hang on, I thought we were talking about Opcache rather than MUC? Anyway, there will always be trade-offs with whatever combination you go with, the trick is understanding and testing so you pick the right setup for you.
I've used APCu for MUC, and sure it is fast. I don't think you could use it for clustered setups, and the lack of LRU expiration and the purge on fill behaviour makes it a volatile choice if you don't understand it.