I know someone who has a heathkit tunnel dipper. I’ll ask him to post about it here. Not sure he will as he’s allergic to his PC. AFAIK his dipper doesn’t work. This might be in line with your point about them not being very good.
I’ve had a large number of tektronix scopes with good tunnel diodes in them go through my hands over the last couple of years. I have played with some surplus tunnel diodes on occasion and found them to be tetchy and difficult to drive. My experiments were mostly limited to attempting to use them as pulse generators however and plotting the curve of one. I’ll leave the latter here as it was interesting:
