The cart in the picture is called the Millenium Mini and was designed by an Australian man, R.J. Walsh, who owns Regal Sulkies. His website is www.rjwalsh.com.au. It was designed mostly as a dog cart and there are 3 types currently and I think another one is soon to be released. It apparently has a very smooth ride with special suspension.
I thought about getting one of these carts (before the harness was designed by Chimacum and there wasn't a good horse harness for it) but was concerned that the end of the dorsal hitch which clips to the harness might at some time bounce and hit my mini on the back when going up or down a hill or in a rough indoor arena or bumpy ground. The negative balance only works if the rider is stable and not leaning forward which would push the end of the dorsal hitch down onto the horse's back. Also, if the clip fails I don't think there is anything else holding the cart onto the horse.
My mini and I are very green and it occurred to me that he would be able to spin around and almost be facing me in the blink of an eye and it would be difficult to turn him back around (facing forward) without getting out of the cart. He used to do spins like that when I was ground driving him.
I'm not sure that horse shows would be very welcoming of the unique design. I think it would be okay on a very flat surface with a well-trained mini.
I want to make it clear that I have never driven in this cart or even seen one but have read quite a bit about it on the internet. These are just some thoughts I have had and maybe I am mistaken. I would also be interested in hearing from someone who has driven in the Millenium Mini.
OH!
