I have 3 BITX40's. The first one had loose toroids flopping about and it worked for a while but I tried to tighten up the toroids and it changed something and I no longer could tune the analog VFO to 40 meters, so I bought a second board with one of those newfangled Raduinos. That board had a broken toroid wire, which I fixed. I got that one working but did a few mods to it, changing resistors for less drift and due to poor soldering work had variable audio output. I then ordered another board and a Raduino for the first board.
I got board 1 to work with the Raduino and installed it in a case and it seems to work well after I went through and tapped all of the solder joints that I had worked on and found one cold joint that made noise as I gently tapped the resistor. With a little heat on the solder joint, board 1 was working well in its case.
I got board 3 to work but had intermittent problems related to my case and installation, later I found a solder blob grounding the speaker to the case, which was also grounded to the antenna. So after removing the blob, things worked much better. I also did the 13.8V power supply thing and was lucky enough to shut down the radio before any damage was done. I installed a really nice PTT switch out of my junk box on the board 3 case, oops, it was a normally on button which caused me to blow the IRF510. After installing a new PTT switch and replacing the IRF510, board 3 works great.
I built a BITX40 repair station which is a piece of wood with Raduino, pots, speaker and connectors set up to allow me to work on a board. It has a 12V power take off so I can use it to build an AGC and experiment with 20m bandpass and lowpass filters. It is set up so that I can take any of my boards and mount it and have easy access for testing probes, or working on the board. I installed board 2 on the repair station and it seems to be working OK now. I will soon be modifying it so who knows how long it will be working.
I think that if you have a good case and good solder joints on your connections, the BITX40 can be a reliable radio, as long as you don't take it apart a lot and change things. Most of the problems that I had were related to poor building techniques, which caused me to learn how to do better.
I really like that case, I think it will make for a much more reliable radio. A lot of the problems I had were related to poor self-built case design, not enough clearance, forcing connectors, squeezing the Raduino in and out. A ready made case solves a lot of problems. I may need another radio to build one of those, it would make a nice mobile rig.