FlexCU has lower output power by 1.3dB for GMSK in comparison with ECU and 2.3dB for 8PSK. FlexCU could double the capacity in the same footprint. But take care about combiners. For (F)DUAMCO 4:2 is the limit 4 logical TRX. And also be aware about COBA. For COBA2P8 could manage 8logical TRX and COBA4P12 could manage 12logical TRX. For bigger configuration you need COSA module.
FlexCU is possible also to use in EMICRO II but with proper setting of parameter CUCONF (output power is lower). It is due to emission of heat.