I've fitted crossfire two three quads in the past (1 emax AIO & 2 iFlight F4s) and I just wired up to a spare UART RX/TX and away I went. Telemetry just worked right away. I've now got a Matek F405-OSD and i'm reading up about needing to do soft serial resource mappings to get telemetry working.

http://www.mateksys.com/?portfolio=f405-...-smartport

The links do seem to just reference FrSky so I'm just wondering if I need to concern myself here.

The Matek docs say there are 5 UARTS and UART 2 is hard inverted already so I just need help deciding whether to go into UART 2 or just another random spare one

You just need to wire up your Crossfire Nano RX to a normal UART and it will just work. I have a Matek F405-STD with a Crossfire Nano wired up and working fine on one of the standard UARTs. All that SoftSerial remapping stuff is for FrSky receivers only. I had to do all that before I switched to using Crossfire.

Ha you beat me to it. I just saw your old post about it so I will avoid the inverted UART thank you

https://intofpv.com/t-crossfire-nano-rx-...on-diagram