I've been following the QRP Labs website for a while and reading the QDX material posted on their site. While the QDX is not quite the definitive stand-alone all-digital-mode radio, it is a very credible development which does many things right - such as recognizing that analog transceivers and linear amplifiers are neither required nor optimum for many digital modes.
There's a lot of very useful background information in the article by Hans (G0UPL) at:
https://qrp-labs.com/images/qdx/fdim2022.pdf The method of determining the "audio" offset is interesting and I'd be curious to have a look at the very near-in JT mode spectra to compare them with typical analog transceiver spectra. I suspect they are much improved, as in many all-digital exciters. Analog exciters (transceivers) are often beset with far more artifacts than most operators realize, simply because they don't measure them, nor check secondary decode levels etc.
One other commendable aspect of the QRP Labs development is that they are making monoband transceivers available for 630 and 2200 m (recognizing the difficulty of very wideband switching in the multi-band units), continuing their support for an LF/MF community often ignored by the likes of Icom and Yaesu - but not Kenwood, Flex, Elecraft, and some others.
One comment I would make is that the QST review is very poor. For a novel, low-cost and potentially popular kit, I would have expected a more detailed lab review, looking at some potentially interesting points of differentiation with the traditional way of doing the signal generation, transmitting and receiving. For example, there are no near-in JT-mode spectra, nor any quantitative measurements of receiver performance. Fortunately, QRP Labs do post some pretty decent transmitter test data on their site which, with a bit of interpretation, presents a fairly favourable view of that side of the radio.
73, Peter.