The one I like is non-digital. Its a hair hygrometer called a Haar-Synth, made in Germany. Its quite cheap (equivalent of $25). The good thing about this one is that you can wrap it in a wet cloth then after a while you can set it to 95% by turning a little screw. After that it is very precise and you can re-calibrate it like this whenever you wish to keep it very accurate. I'm making it sound more complex than it is.
Also you don't need batteries for it. And it can take a reading in 2 minutes.
Personally I like the non-digi ones.
Hi there, yes I've used these kinds of hiding places with no problems and I'm quite sure its fine. I also use upside down plastic flower pots with a hole cut in them (to get in and out).
I'm certain that Aspen shavings are good but I do not know about Cypress.
Here in the UK lots of us use hemp but I believe this word is not acceptable in the US, although the stuff we get for our torts is no use for anything apart from tort and horse bedding.