I use SmartCalm too. I used to have my mare on regular SmartCalm plus U-Gard after she had ulcers as a preventative. My vet and I could only assume that her ulcers were from her stressing herself out because she has some serious anxiety issues.
Since it had been two years since her ulcers have healed and she's been pretty alright, I took her off U-gard, but wanted to still have a bit more prevention. SmartCal Ultra has twice the magnesium, which is also helpful with treating ulcers, so we switched.
She's even less spooky now and hasn't really had any "panic attacks" since. I will add that she is not derpy or deadheaded. If anything, she's been hotter to ride, always wanting to run around. But I have started doing cavaletti with her and she's been more focused on the task at hand after a quick correction regarding whether we are in the Kentucky Derby.