I don't have the 300 Fireball from Model 1,but I do have a couple of their 223/5.56 uppers and they are well made and shoot right with my RRA AR15.
They only offer a 1-8 twist in their 300 Fireball so you will not be able to stabilize bullets (supersonic) from what I've been told. But from all the research that I've done,nobody makes a barrel with an in between twist like a 1-10. You either have to get a 1-12 or a 1-8 twist. So you can either shoot subsonic rds or supersonic rds,but not both with the same upper.