Not that long ago Forbes posted an article about cannabis for migraine prevention. It got ignored by all the headache advocacy groups (for SOME reason that I will let you all figure out on your own) but I am posting it here because it did include some cluster sufferers. It was a small study but it found that half of the cluster sufferers had better luck using a THC/CBD combo than using verapamil. It was a whopper dose, from what I can tell it looks like 100 mg THC and 100 mg CBD combined. One interesting thing that was noted was that the cluster sufferers who got relief were the ones who had migraine as a child. The study was done by Dr. Maria Nicolodi, an Italian researcher that I have been following for a while. I have a lot of respect for her and have seen a number of valuable studies done by her. Here's the link- https://www.forbes.com/sites/daviddisalvo/2017/06/29/marijuana-treats-migraine-pain-better-than-prescription-medication-study-finds/#73190af53700
And here is some more info on the study- https://www.ean.org/amsterdam2017/fileadmin/user_upload/E-EAN_2017_-_Cannabinoids_in_migraine_-_FINAL.pdf
In regards to anecdotal experiences, I know one person that has had multiple brain surgeries that were not very successful but he has now gotten relief by vaping CBD as a preventative. On the other side of the fence is me, if I take CBD it is one of the worst cluster triggers I have. High dose THC works pretty well for me at times but I stay the hell away from CBD at this point. I am pretty sure that in this regard I am just (once again) the oddball. I have not met anyone else that has ever said that CBD triggers their clusters.
Hope this helps.