I did! A saison and it worked out well. For the calendula I added around 1oz to a 5 gallon batch at around 5 min, pulled it out at flameout.
My thoughts. It's subtle, and especially with the I'd of other flowers (chamomile, nasturtium) its hard for me to distinguish which favors this added specifically, though the beer definitely has floral notes. I'd say, don't be too hesitant for quantity, I was and I think I could have gone bigger and been fine. Hope that helps a little.