And I'm not big on fishing
When there is a need for knowing the depth, a depth sounder can do just that. And no more.
A fish finder provides a whole range of info like the shape of the bottom and the make-up of the sea bed (rock, sand, etc). Many of the better ones have forward-looking sonar that is also very useful.
And it can also see fish if that's of any value to you.
Not to mention shipwrecks, big rocks...they are fun to twiddle with. I got a monochrome Eagle fishfinder for the nav station because I could make the numbers quite large, large enough to be read from the cockpit. I kept the old, still functional cathode ring one as a backup, but really, I use the new one a lot more.
Another trick is to set the alarm for a known depth contour, like 10 metres or 30 feet or something that will stick out on a chart. Then you can follow the contour in fog knowing where you are not
, if you follow, which can be quite helpful. For instance, if you find a nav aid that your DR tells you is near, and it's close to a known contour, you can be in fog at night and find it, and then literally get your bearings.
I'm no Luddite who would turn down a chartplotter, but give me a paper chart, a fishfinder (tells me when I've hit "shelly bits" or some unusual charted bottom state) and a compass, and I can usually find my way to safety.