If I understand this correctly, all the Linux-based quad-radio systems are "sorta" full duplex.
A true full duplex system puts data down the transmit channel, and gets everything including acks, back over the receive channel.
The Linux-based systems still get their acks back over the transmit channel so both channels are transmitters and receivers, although the DATA flow in one direction only per channel.
This "quasi-full-duplex" has a number of practical impacts.
1. It slows the channel slightly
2. It means that you still care about the receive capabilities of the transmit channel at the transmit end. Noise levels in particular comes into play here.
3. You can't play silly games with EIRP rules, where one end of the link uses a small antenna and low power to transmit legally, but the other end uses a big antenna to receive as no transmission happens at all. Works very well with a 5.3 / 5.8 split in FCC land, Wmux has been doing it for years.
Still a very good tool for many situations, but not the real deal just yet.