These little QRP transceivers first made an appearance some 20 odd years ago. They are extremely simple transceivers that use the TX PA as the RX mixer to save parts.
I built a Micro 80 some years ago and my best QSO was around 300km. Biggest issue (for me) was broadcast breakthrough from strong broadcasters just above the 80m band. Variations included the Pixie 2 which added some refinements at the expense of more parts. Kits are available, but the circuits are so simple it is not work paying over the odds for these. The Micro 80 uses all discrete components whereas the Pixie and Pixie 2 use an LM386 for the RX audio.
If you build one, be prepared to fight for contacts. It is not the TX power that is the problem: it is the receiver that is the limitation.Given good conditions and little broadcast breakthrough, these rigs work.
The same basic schematic will work on any HF band with changes to the output filter. Watch out for chirp on the higher HF bands: don’t be tempted to try to pull the crystal too much, especially on the higher HF bands.