Product review (5 stars): Great for guitar cases, darn accurate!
This isn't the most expensive hygrometer available, but it's accurate as far as I can tell. It's reading temps accurately and passed the 'salt test' after 20 hours with flying colors, the final 4 of which were completely stable at 75%. Threw it in the guitar case and it leveled off within 3 hours and hasn't moved from 70deg, 49%rh. Just what I wanted, perfectly good option for a guitar case IMO, there's no need to spend any more.