We have a mare at our yard who has taken them for about the last 5 years over the summer months and they are great. Her headshaking is much better and she loves having the biscuits as a treat everyday!
Yes, I use them in May when the rapeseed is in full flower. I'm not entirely sure they work but they have the additional benefit that both my horses will follow mer to the end of the earth if I have them in my pocket... and that includes into a trailer! Tra la la! Loading problems totally solved!