I have an RSPdx and use SDR Play running under Windows 10. It works pretty well and I use mine quite a lot on MF/LF running with WSJT-X. To do that I use VSPE for the "CAT" control and Virtual Audio Cable for the audio routing. That all works fine, and is quite robust. SDR Play has some odd non-ham labeling and operating conventions but, once you get used to it, it's quite functional and relatively easy to use. Although you can use other SDR programs (e.g. HDSDR) instead of SDR Play, you lose the ability to set some of the receiver hardware bandpass filtering below 2MHz. Since that's important to me, I've stuck with SDR Play.
So far as the receiver is concerned, it's quite good. I would say it's the modern functional equivalent of a (very) wideband 1970s or 80s general coverage receiver, although with greatly increased capability relative to the older receivers. I've run mine in parallel with a TS-890S in order to do some evaluations in various modes (digital and analog) and, while the RSPdx is not a patch on the 890S's overall raw performance, it's pretty good for a radio less than one-tenth the price of the Kenwood.
Regarding the manual, my biggest complaint is that there isn't a decent succinct write-up of the system, with too much being shunted off to rather basic videos with incredibly low information density.
Overall, I think the receiver is good value for money and a few of the add-ons (like the free spectrum analyser application) would be quite useful for hams without much test gear. It's like all such systems in that you have to be conscious of the somewhat limited raw dynamic range relative to full-fledged communications receivers, and be cautious with gain setting etc.
73, Peter.