I'd rather be effective than right, Dry.
Well the fact that 12 of 20 texted/emailed me to say go ahead and one emailed to say don't shows me that most weren't "binned" before reading. When I then called on the remaining 7 most of them thanked me for my letter and all said carry on cleaning.
Don't forget these (mainly elderly or at least 70 plus) people have time on their hands and might like the novelty of actually (gasp) getting a "real" letter.
The OP asked if anyone had written letters. I had. I responded. Hopefully he and others found it helpful.
Some including you felt the need to express your views that it was too long winded etc. And so I have answered those views in a thorough (and too long winded for some) way to show how the letter was effective.
Horses for courses.