I have often used Calm and Cool pellets for stall rest/injured horses. At the recommended dose (a scoop AM and PM) it did "take the edge off." Just the edge. Didn't turn a fire breathing dragon into a puppy dog, but helped. I saw noticeable differences in many horses, not only my own.
I have occasionally used a double dose (so two scoops at once) or triple dose (3 scoops at once) for my stress-ball when I knew I had to trailer him somewhere or when I knew life would be stressful for him (4th of July fireworks, etc.) It helped. Again, just took the edge off, but sometimes taking the edge off is good enough.
I have no experience with the daily Perfect Prep. It's expensive!
i have used Quiessence and Total Calm and Focus. Both have magnesium as the primary ingredient plus vitamin B. I have really good success with both. The Quiessence did "reve" up my guy for a day or two and then he settled right down. Magneseim is the ingredient you want, not so much all the herbal stuff. Never had much luck with that stuff.