I've taken KPV several times now. Initial dose was 100mcg which gave me some brainfog.
Then I tried 250mcg once a day to check for side effects. I had no side effects prior to my bacillus subtilis hu58 crash, but afterwards intense burning in my lower intestine (it was below where my stomach was) and headaches. However as my crash has resolved the burning seems to have almost gone. The burning was almost stimulating my appetite and I think that's why it gave me headaches.
This stuff is amazing for immune based inflamation, it completely knocked out immune based inflamatory pain when my crash began, reliably after every single dose for about 4 to 5 hours.
The burning I believe was due to some affect on microbiome composition, maybe killing bacteria that shouldn't be there.
As for the MCAS side of things verdict is out on that front. BUT I am not experiencing my usual crash this autumn when putting the heating on. I live in a new house however I think this is due to the prebiotics I've taken and not the kpv, as the prebiotics confer a long term change, whereas kpv only lasts 4-5 hours.
So overall didn't make me worse or miles better, but was great for immune inflamation.