We used the NAF Magnesium one - the only proof that it worked was the fact that a horse which had never loaded successfully before walked straight into my trailer and travelled well for 45 mins to a new yard. I would add that it wasn't my horse and I had never handled her before so there is always the possibility that the 'issue' was handler related.
You could always have a trial run.
i use the global herbs one for my mare,she had an accident in the trailer and after months of using a monty roberts halter and lots patience she now travels but she has to go on her own and still gets stressy,it def chills her out,give it an hour before travel for max effect.
Well, it took us 6 hours over 2 days......the calmer just made her dozy so we ended up with her half way up the ramp falling asleep!!!
In the end, my mum got behind and shouted...and she went straight in! I do wonder whether she just wants to see how long she can not go in for......
She does move around a lot when travelling and has an injury to her fetlock that the vet can't explain(from before I got her) so I wonder whether she's been involved in an accident....