I don't feed comfrey. I learned to leave that discussion alone on this forum a couple of years ago. Basically, if I wanted that much drama, I would have started a thread on abortion, politics or war.
At this point, I will say that I view comfrey more as a medicinal herb with potentially toxic side effects, than as a forage. As a forage, you are not losing anything that you can't get with other forages. There are differences between strains/varieties and their levels of toxins, which only muddies the waters, when personal experiences are shared. The actual content of a strain/variety, the amount consumed, how much is consumed and the species consuming it are huge variables. Over the years, I just always tell people that are interested in comfrey to read up on it, so they are informed of the risks.
My chickens forage in an area that was sheep pasture, with grasses and legumes growing there. They have other areas they forage, where I have planted bulkier leafy foods. Plus there is woodland area, that has a lot of leaf litter. Plus they hang out in my yard by the house, with all the things planted there. Mostly they behave, sometimes, not so much.
I would be tempted to give them a small area planted with some of the non-pasture plants. I think chickens do pretty well with straight pasture, mine used to be in with our sheep. I also think you could do more if you were interested in giving them more variety. The forage you provide can be strictly about nutrition or it can also be about the richness of their environment. It just depends on what you want to do. I know one of the people here even had chickens that would eat the beets in the ground, later in the year. After they ate the tops off, they ate the beet and would scratch around to get at it. I thought that was interesting.
I know a lot of people are interested in these thread topics and have different goals and different sized areas they want to plant. I think it also makes a difference if people just want to pasture meat birds or if they're wanting to do something extra for their pet hens.