I have the same one. It’s interesting. I wasn’t really sure it was needed. I live in Ohio. We have central heat but no in house humidifier. After reading about the ‘need’ online, I decided to buy a cheap meter that shows humidity and temperature. It showed my house was 20-22% relative humidity. So I bought a hard case and the OH-18. In the case, the humidity went up to about 40%. One thing that I noticed was before the humidifier, if I ran my hand down the edge of the neck, I could feel the edges of the frets slightly poking out (and was surprised as it’s a pretty good ukulele). After a few days in the case, the neck was totally smooth so I guess it had shrunk in the dry house. The tuning changed more at first but then stabilized. So I guess this humidity thing is real!
Jerry