I’m running the BlackMagic UltraStudio Mini monitor. I had to buy this so I can run FCPX, Premiere, AE, and of course Davinci Resolve (due to Resolve not seeing AJA). For the most part it works fine except once in awhile if I switch NLEs or in and out of Davinci my monitor goes all crazy. Only way to fix is if I quite everything and replug the Thunderbolt from the Mini monitor. If I wasn’t working in Davinci I probably would have bought the Aja T-Tap instead.
Also, if you are changing frame rates in between projects you have to set it inside System Prefs and not inside FCPX. That drove me crazy before I figured that out.
Hopes This helps.
J