no no no - mmcx is good on 5GHz, but on SR-5 mmcx's are no as good as Ufl. We tested this on about 10 "different" SR-5 (from other distributors, not a same time) and the result was that...
UFL is better than MMCX on SR-5 about 5dB!!
Of course we have our own UFL - Nf (or Nm or RSMA) with special ultra low loss degin:
I think that is hardware diversity problem for UBNT card, because even if i will change antenna-mode to MMCX in MT some signal is transmited on ufl - I know that's normal, but on UBNT this signal was too high comparing to other atheros and their diversity.
and we need to use ufl...
as You can see the motherboard on top have 2x SR-5 (1 and 3 slot)
this is more detailed image: