From my experience I haven't seen a huge difference in hygrometers when it comes to expensive and inexpensive ones. The one that I liked the most is the Diamond Crown one. Though the Diamond Crown was the most expensive it was spot on the correct humidity straight from the box. I picked up one from Heartfelt and it had a pretty bad reading, something like 15-20% off. I think the Heartfelt was ~$10. I picked up another small one that is an adjustable puck and off the bat it was +5% but its adjustable so I corrected it accordingly. This one ran I think ~$10

As far as analog hygrometers I have never seen one that is accurate. So I usually stick with digital ones as much as possible.

As far as the cedar goes, the sheets that come from boxes are safe to use in humidors. You can also use the sheets they wrap around certain cigars. The sheets are good for separating cigars from each other and adding some material to retain a little humidity in humidors.