LONESTAR ELECTRONICS ( N5BOC Store ), US maker of MMDVM modems both Simplex and Duplex which become the engine of hotspots running PiStar for DMR, Dstar and Fusion.
the ONLY one which keeps the Pi Zero form factor that has become so popular. This will enable you to keep the portability of the MMDVM_HS_HAT while at the same time allows you to enjoy the benefits of a DUPLEX board. For DMR this means it can have QSO's happening on both time ...