Well, I've always stuck with the stable release - but yesterday I bought the Mig and tried to install it and got an error. So I bumped up to the latest open-beta and it installed OK.
So the Mig might not be available, yet, for the stable version. I've not heard anything official - and the store makes no mention that it only works under the beta, which is a bit naughty.
I think tomorrow there might be an update for the stable release - but that's just a guess.