Generally people are asking for trouble if they try to go from running moderate to high mileage in trainers to running the same mileage in flats.
But there's multiple ways to manage the transition. Posters here have done each of these, and maybe others:
- work your way gradually down, in a series of slightly lighter, lower-heeled shoes
- sneak the flats into a rotation with your trainers, and gradually increase the % of your miles in the flats
- make an immediate total switch, but radically cut mileage to what you can handle in the flats, and build back up
Whatever you do, there's an element of "listening to your body" - as usual with running, there's no one-size-fits-all formula.
I suggest when you start with flats, use 'em initially for the *easiest* running - short recovery runs, maybe even walking around - for a smoother transition. If a shoe is different enough from what you're used to to pose an injury threat, why start with the hardest, most stressful running in it?
That's all generalities; I'm totally unfamiliar with the Brooks Launch.