As with guitars, I have multiple versions of different styles of hygrometers. And, over many years, I have possessed many, many more of these devices. My own experience with hygrometers has led me to a slightly different conclusion...
Digital hygrometers are inexpensive, small and relatively durable. In other words, they fit in most guitar cases, not to mention most players budgets. It is no wonder to me that many guitar manufacturers recommend them for their consumer base. By contrast, a quality analog hygrometer is expensive, large and relatively delicate. It has no business residing inside a guitar case. I am not referring to those cheap 2.5" diameter plastic encased dials, either.
It is recommended that analog hygrometers be "tuned-up" very 6 months, or so (a simple process), where most digital hygrometers have no adjustment capability. Regarding accuracy, there is a bit of myth that can easily be busted (ask me how I know): purchase 11 or 12 digital hygrometers (or 30 or 40) and set them side-by-side. If you wondered if I was going to insist that none of them will agree with one another you would be disappointed, as one or two of them might actually agree. I am looking at 6 of them during this writing, and they differ by 12%. YMMV. By contrast, if you can afford it, repeat the process with expensive analog hygrometers, ensure they are properly tuned, and you will be surprised at the consistency.
I rely on an analog hygrometer (maintained) as my standard regarding Relative Humidity; it sets the mark. I note the deviation in each of the umpteen digital versions I have at any particular point in time so as to have a better (closer) representation of a given RH readout.
All that said, the most humorous part of my fixation with the inexact science of accurately determining Relative Humidity right here, right now is that it doesn't really matter as much as I wish it did. Sudden, drastic changes in temperature and prolonged exposure to humidity extremes are what damages guitars (and houses and people and other things, too). I'll be back after I go tune my hygrometer...