Rotating vane sensors work very well, but they do take away from the bin capacity. I picked up a used vibrating rod sensor and have done some prelim testing and it works consistently and takes very little in the way of height. I just have a 35 gal. bin, so can't really afford to lose any.
I have the old Oneida mechanical sensor that spins and it works great once it senses the bin is full it sends a signal to a flashing light inn the shop. Not sure if they are still available but definitely works well. The only down side is it hangs down about 5" so reduces capacity.
That makes sense, but I'm a hobbyist, and I generally do a little work one day, and later do a little work on something else, and so on. So there's no real good end-point to check the dust collector. And there are other people who use my shop. So, for me an indicator makes sense. "When leaving the shop, check the indicator" is much more convenient than, "when leaving the shop, dis-assemble the Frankenstein dust collector and check the bin."
As you say, personal preference.
Personal preference. I have tried indicators in the past. Now I just think about it like the paperwork at the end of a job . . . you're not done till the paperwork is complete, right? At the end of a project or long session of milling I empty the bin. Every now and then I fail and get the result we all dread but mostly this expected step of the workflow works.
I had the iVac sensor on my old pre-Gyro Frankenstein dust collector, and it worked well enough. I was using black contractor bags inside a metal trash can. The sensor has two green LEDs, two yellow, and a red. In a perfect world it would show no lights when empty and all lights when full. In my case it showed two green when empty, and I learned to empty it when it showed two green and two yellow. At that price, I'd buy it again.