If you plan on hitting up a drag strip quite a bit you'll want them. It's the hard launches and wheel hop that kill them. I've done a full bmr suspension setup to prepare for the extra power.
Yeah a dealer by me quoted me $9624. I gave them a big ol nope. Lol. Found the phase 2 kit on Levittown Ford for $6600. Then around 10 hours of labor if the dealer does install.
Magnuson already said it will be available for current gt500 as an upgrade and they stated it'll have current Gen LS versions. Those are all coming to market early 2021. Don't think Roush will sit on them til the new mustang platform.
I was very close to ordering a kit today but saw the news about the new 3100 head units coming next year replacing the 2650s..... Hopefully roush releases some news soon