While I really appreciate QRP Labs and their ProgRock and ProgRock2 devices, and have used and recommended them several times myself, I would point out two issues that often need to be considered when using them.

1.  The output signals are not "clean" in the sense we usually use that term.  The output signals are very rich in harmonics, and in some application that can be a problem.  QRP Labs offers inexpensive low-pass filter kits that will knock down those harmonics and produce a sine-wave signal I would call "clean".

2.  The programmable microcontroller on the module itself sprays significant noise that can bother a receiver.  Last year I set up a ProgRock2 to act as a crystal substitute for an FA-8979/TRX-102 transceiver that I wanted to use to listen to the local airport VHF AM frequencies.  The interference from the microcontroller IC rendered the receiver unusable.  I tried shielding the ProgRock2 module and bypassing its power wiring but the noise seemed unstoppable.  This may not be an issue for HF receiving - I've not tried that.  My applications have been VHF/UHF equipment so far.