Although I have always been a Blue Circle fan, I have to say that a current situation I am going through right now has left me almost to the point where I will not recommend their product to anyone. We'll see how it plays out, but if things do not improve, they will definitely be placed on my AVOID list. I will elaborate in the near future.
Sonically, the amps are quite different, and it seems to be an easy choice. It simply comes down to a question of sonics and your tastes. The MF is much more "neutral" - whatever that means, faster, and a whole lot more extended at the frequency extremes. The Blue Circle is more relaxed and liquid. If you prefer immediacy, slam, and neutrality it is the MF. If you like more warm and lush, BC. Normally, things aren't this easy, but these products sound so different that this time it is.