In the forced rotation camp there is another choice as well, the Makita PO5000C. I have one and it's been my only experience with forced rotation thus far, but I love the thing. It is similar to the Mille in that it has a smaller orbit (5.5mm for the Makita, 5mm for the Mille). I actually like that it has a smaller orbit combined with the forced rotation. You can bring the edge of the pad right up to panel edges, like under a window seam or near some plastic body trim. It's a very precise tool and well balanced. It also goes up to a really high RPM relative to the competition, so it can cut extremely well even with its small orbit. I imagine the Mille would be very similar, but with clockwise pad rotation and a little less top rotational speed.
The Makita is also built like a tank, and made in USA. It does have a switch to change it into a free spinning orbit, but I rarely use it as it really stalls out easily. Probably useful if you were to use it as a sander on gel coat or something.
The Flex has an 8mm orbit with lower rotational speed, so it can cover a broader area a bit more effectively and act more like a traditional orbital polisher with some extra horsepower. Really it all comes down to personal preference.
