Bob Benedict, KD8CGH
The uSDX is a development effort that has several evolving designs, it's not a single product like the uBITX V6. One cool aspect of it is that it uses a highly efficient class E amp not only for CW, but for other modes too. It pulls off this wizardry by pulse width modulating the power to the amp. It's a uses direct conversion SDR receiver with the rest of the signal processing done computationally. The amazing thing is that all of this, including A/D and D/A, is all done by an Arduino so there is a very low discrete parts count.
It started single band as a modification of QRP Labs QCX class E amp CW transceiver. The two main design streams now have multiband filter boards.
Check out the uSDX group.io WIKI for an overview.
I built a uBITX V4, a WB2CBA uSDX and I'm slowly building a DL2MAN version uSDX (I'm not so good with SMD). In my opinion, compared to the uBITX, the uSDX has more features like AGC and variable filters. It's better at CW since it's QSK and has filters you can narrow, but the SSB transmission is not as good. The uSDX firmware is evolving rapidly, like in the early uBITX days, so we'll see how it progresses.
BTW Farahan often participates in uSDX discussions. I wouldn't be surprised to see a new transceiver from HF Signals.