You do realize the new Flex hasn't been out more than a day or two now, right? Nobody has them yet to have tried them for a proper or reasonable review.
Well Evo, I'd get the DeWalt, it's about half the price, got a proven track record. And although Flex gets a pass from many, I didn't care for their DA, and some of their rotaries had some issues as well. That's not to say that this new wonder isn't all that, for what they're charging it better be!
I'm a huge fan of Dewalt tools and ran their rotary for several years without a problem. I think my next high dollar rotary is going to be the new 3M machine.
Mike Phillips got one last fall and posted a video of him using it over on the AutoGeek site. Several guys over there have received theirs so a review should be up shortly.
There was a guy that went to SEMA and said DeWalt was coming out with another rotary that had a 600 rpm start speed and was lighter. It's suppose to hit around June-July. I would have waited but I got a great deal on my DeWalt and it was something under the old Christmas tree that the kids wanted me to have. I've enjoyed using it and will get more time on the trigger as the weather gets warmer.