My Quad is probably my most valuable training tool. I equate it to swimming a horse, but with better benefits. If you read Ambrose's previous posts you will remember that he was ponied for two weeks before he was even put under saddle. I learned how he travels, if he is going to be scared of things and shy, how fast he can trot, if he is sound. What I find is that they will usually take a day or two to get used to the idea and you may have some setbacks along the way, but once they get the hang of it, it works, and works well. I can build bone density, cardio, and get a horse legged up without the added weight of a rider. It gets the horse used to the area you are going to ride him in so he is not acting stupid when you do have them under saddle. It is a good way to keep or condition a horse in between those training rides. I have built MONK's speed up from about 13mph to 17mph just on the Pony, it is not unusual for his HR to reach over 200, he has increased his trot to almost 19mph, he cannot do that under saddle but he will do it running free, he will hit over 24mph on the hills. I use the Garmin transmitter on a polar chest belt so I can check HR's and speed, this works great as the Garmin has maybe a 30 foot range.
I have on occasion even ponied MONK 20 miles.
I will have a whole section on boots, as all my horses are barefoot horses, but all these works are done in the EasyCare Inc. Gloves. I am not sure I would even attempt to Quad Pony without them, the concussion would just be to great unless you have a very forgiving surface.