Owain wrote:
Pete Verdon wrote:

Is it just that the current flow is very small, and almost all the
voltage is across the neon? Can anyone with a better grasp of
electrical theory explain?

Basically yes.

Thanks. That's what I was asking.

They are too likely to fail dangerous and hurt somebody, and too likely
to give a false positive or negative, that they are completely unsuited
to the tast and not fit for purpose. A proper electrical tester is much
better.

I went to some length to make clear that that wasn't what I was asking :-)

Pete