I would be concerned about…

I would be concerned about the rigging for the manure bag getting stuck or caught on a tree branch or bush while riding on the main trail, and off of the main trails causing a horse to have a bad spook, possibly seriously injuring the horse and/or rider....not to mention trying to train a horse to wear it...it looks like it's not too comfortable for them.This would also inhibit the horses natural ability to swish their tails at flies and other bugs to avoid being bitten, while being ridden which again can cause a reaction from the horse which could lead to injury to either horse and/or rider, not to mention the possible damage to very expensive tack on the horse should they get bit and have a negative reaction to being bit.
Horses are living,, breathing animals that have a brain, even the best trained hirse can spook or bolt and cause injury on any given day, and i and I am sure like myself, other riders feel this rigging and the manure bag will cause more negative issues than a few piles of very biodegradable manure on a trail .