I ordered some of the Grounds product from Tractor Supply and am waiting. I'm in Los Angeles and I don't think Rural King will ship to me. We are rebuilding our coop and it will be 80ft2, so price will be an issue, not to mention availability. I reached out to the company to ask some questions-no response.
Didn't you say on your blog or something you are using grounds from local coffee shops/your kitchen without further processing? How is that going? The article I think you cited did say chickens that had coffee in their diet had thinner eggshells, but it didn't say anything about bedding. I have done a quick internet search and once-brewed coffee still has quite a bit of caffeine, but how much do they consume, directly or indirectly? I've tried reboiling and cold rinsing my old grounds and, well, it was a mess. We drink a lot of espresso here too, and there will be no second rinse of that product!!!!
The test would really be what happens in real life. As I think you noted, the volatiles oils in pine are pretty toxic/caustic to human respiratory systems and people use them right and left. Just like everyone says "don't use cedar" while not even thinking about how toxic pine is, I have to wonder about coffee grounds.