M&M is worth reading after Baby Miller. It's "readable" in that normal people can sit down and open up M&M and read it. Barash and Big Miller are more reference materials. I guess some people sit down and read the big books but I'm not one of those people and I don't personally know anyone who says he is.
When I started my written board prep in earnest, I would do questions (mostly Hall and the ABA's released old exam questions) and look up references for each one in Big Miller. I never sat down and read a chapter of Big Miller, though I've spent more time reading Big Miller than I have M&M. But I've never been a sit down and read kind of learner, if there's no directed focus to what I'm looking up and reading (like a board question) I don't retain things well.
In the end it probably doesn't matter what book you choose as long as you use it frequently. They all say the same things. Eventually you'll want one of the big reference books like Big Miller, Barash, or Longnecker. M&M says more things than Baby Miller so it's worth reading if you've already plowed through Baby Miller. I would encourage you to incorporate specific board study into your reading though, even as a CA1. The AKT-6 is coming up and there's nothing like a good AKT-6 score to get the Man off your back ...