I thought comfrey was supposed to be cut down before flowering for best results. On GW last night, Alys had left hers until it had finished flowering, so that the bees had the benefit, which made sense to me. Is there any reason not to let it flower, unless it's to avoid self-seeding? Mine's Bocking 14 so not a problem.
The only reason is the self seeding.If thats not a problem for you,let it flower and then cut.....I only have a small area to grow the stuff so I tend to cut long before any flowers appear.
I always let mine flower for the bees then cut it down and add it to the compost heap. I did it about a month ago and it's grown back and about to flower again. :)
Good. Mine had flowered before my first cut anyway, will leave it longer for the next one.