At the risk of sounding like I work for Blue Chip this stuff is amazing. I've been using it on one of mine for about two weeks. He's not difficult or silly but can be very spooky and winds himself up easily. He gets bored easily and struggles to concentrate. And when he spooks you have to be awake as he's so quick.
I got fed up of always having to be on the look out for spooky objects and his constant jogging when fresh so I decided to try BC Karma. I'm sceptical about calmers in general but have heard good things so thought it worth a try.
I can't even begin to tell you the difference its made to him. Spooking has stopped completely, just the odd gentle shy now. And I can ride him buckle end when before he was jogging and always wanting to go faster. Even after a week off and a whole day stuck inside on Monday he was as calm as anything when I rode him Tuesday. Everyone who knows him has remarked on the amazing change of behaviour. I still can't quite believe it myself. Anyway I've just ordered a load more direct from Blue Chip (they give discounts for orders of 5 bottles at a time).
It won't work for every horse as it will depend on what the horse is doing and why but for my fizzy lad its worked wonders.