I have never used MFW, but we have tried to use boxed curriculum before and it stifles my interest, as well as the kids because it is very schedule oriented, workbooky, and tend to not use the best of the best in literature. Our experience is completely different now that we use the SCM stuff...love the flexibility, the do-ablitity, and the enriching way it helps me teach my kiddos. I thought it felt "light" too, but after using Mod 1 for an entire year with a 4th and 5th grader, I am amazed by and love how much they retained and enjoy to this day. Loving the second year too! =)
I love SCM as it is, but what I really like it that I can tuck in things here and there as I want to and not feel overburdened and behind the schedule- by this I mean little hands-on acitivities, a movie, a field trip, an extra book, whatever I want. I have several things that are just fun to add to both the science and history books - and I would do this with ANY curriculum. It is just how I am, plus the fact that I know my kids and how to help them be excited about different subjects.
HiddenJewel gave you some good advice. Try it and see. It dosn't cost very much and then you will know what path you want to follow.