I'm crazy about mine!! I bought it from Dana Sparks over a year ago and have used it probably 6 or 7 times a week since then. It still looks new, too. I recommend the leather condit. she sells, too - I can't remember the name but it's in a silver can and from Euro. and the only stuff she sells, I think. Way expensive but does a terrific job.
I rode an Arabian in a Jeffries, but I think it was a falcon or hawk.
On that horse it was the best saddle I have ever ridden, I was truly in the center of the horse. I think it was a combination of the saddle, how well it fit the horse and the fact that the horse was evenly balanced between his hind end engine and his front end.
It was an older model saddle but wow.
P.s. My regular saddle is a Crosby equilibrium, so I am fond of close contacts.
I bought one and rode in it for a year. Bought it from John Merryweather who is the JM in JMX. He fit it too narrowly for my horse and I had to sell it and give my horse's back time to rehab from the damage.
Gorgeous saddle with beautiful leather and came flocked with soft and springy Jacob's sheep wool (Though John adjusted it with synthetic wool making the panels lumpy).
I hated selling the saddle but my horse goes so much better in a saddle with a flexible tree and our new XC saddle is the Kent and Master's Monoflap which is just as nice to ride in as the JMX, changeable in case he builds or loses muscle, and less expensive.