I have a FB2, Primo XL, and MB1050. I'm a FireBoard fan all the way. However, I'll say that I like the native controller on the MB better. But, I have no plans to remove my retrofit. The FB is so nice because of the charting and history. The native MB controller is so responsive. I feel like it runs w/ very small temp swings.
The only time that I run the FB2 on the Primo is for longer cooks where I won't be around. Minutes before I saw your post, I was just thinking about running the FB2 on the Primo this year for Thanksgiving. I know... that's a long way off, but I am already thinking about which of my 7 cookers to use! lol
I used to have a digi-q, and if Ultra is anything like it, I'm sure it's a well built product. I don't think you can go wrong with either. Oh, and just for the record, I use the BBQ Guru fan on the Fireboard 2!!