If you are new to the idea of foraging then comfrey is something that can be a bit confusing. It has white, pink or purple flowers, can be used as fertiliser and compost accelerator and is much loved by organic gardeners. The leaves and sometimes roots are mentioned in older wild food and medicinal herb books but newer ones tend to go on at length about the potential dangers and talk of toxic components.
See this article from Monica Wilde which goes into the research, history, pros and cons of comfrey.. it is long but well worth reading. http://monicawilde.com/is-comfrey-edible/
Personally.. I do eat comfrey and have no problem at all with it. Like most things, I believe moderation is the key. The vast majority of people who do eat it are unlikely to have more than a few leaves a month (unlike the poorly rats in the study who ate it constantly for weeks .. and rats don’t normally even eat it).. but it is your choice.
Comfrey is used widely in herbal medicine and homeopathy for its wound healing and bone setting qualities. If you decide to make any medicinal creams or concoctions then symphytum officianale is the one that you need which is the one with white flowers. Most wild comfrey is crossed with other varieties, usually the purple Russian variety, so I suggest you get some ‘proper’ dried comfrey or tincture from a reputable medicinal herbal supplier like Baldwins so you make sure you have the right stuff.