Refractometers are quite useful for pale wort and clear distillation products - or anything where you calibrate close to target phase subspace (honey, must, well-known beer recipe, etc.). I use mine to determine when fermentation rate slows down to determine termination in yeast tests - their relative readings are OK, if they aren't changing, it's worth considering density is stable.
Regarding U-tube, that's fun enough little project if done right. I had even more daring idea to build contactless (read through glass) density scanner, I even have the already soldered and flashed board and transceivers somewhere around the place. The prospect of quick reading density and inner fluid temperature without exposure seems attractive enough, but it's a lot of research work to tune this tool concept, and then to turn it into comfortable product, and I'm kind of short of time-money invariant resource now.
I used to buy directly from beekeepers (never from stores, that junk is just spoiled in most cases). Only from people you get to know personally, beekeepers are the most hardcore underground people around for some reason. They usually sell honey in meadmaking quantities much below retail. Just talk to people around, it's abundant all over the world. And the result is totally worth it.
I've been doing this for over 10 years now I think; had to move out of USA at some point and lose about 300L of product (it has to age, nothing you can do - and shipping alcohol is very complicated issue) - gave it away to friends, this was quite a challenge. Then started all over and over, the oldest bottles I have now are from 2019. The best time to make mead is 10 years ago, second best is now!
Then, recently I became a beekeeper myself. Oh, this is addictive stuff. My beehives are smart homes now, I can listen to the sounds of bees and check their environment from home and I'm going to start selling the system to other beekeepers within weeks. And something like this happens to anyone who gets into beekeeping, it drives you crazy. I won't be selling honey myself for some time though, as I've only started recently and all I get goes into mead I can produce myself until the families grow enough, who knows how long it will take?
At least I've learned the ins and outs of the trade, why exactly honey from somebody you trust is completely different from retail anonymous "local honey" jar in store (or much worse, imported ones). There are quite objective shortcuts that should not be done but are economically attractive.