I have a UPR k member with coilovers in my Mustang and love it. The roads in the town I live in are horrible and it handles them with no problem. Plus the benefits of 100 lbs off the front end of the car and the ability to adjust the ride height to whatever height youd like, you cant go wrong. With the UPR Kmember and relocating the battery to your trunk your mustang will handle like a completely different car. I guarantee it.
You don't need Coil overs with the QA1, it comes with spring perches. I swapped it out for the UPR kit with tubular A's and coil overs though. I wasn't fully happy with the QA1 because it tilted my motor too much to the Pass side and we had it fully adjusted.
I also like the coil overs with the UPR a lot better as well as the motor sits how it should. UPR is the best budget purchase IMO. I have hella speedbumps in my daily commute and not a single crack on any weld and the coating is holding up fine.