From the saddlery website
This saddle is fitted with a flexible tree
Changing the gullet on a saddle does allow for one saddle to be used on horses with different shaped withers. However, it does not address the changing contour of the horses back that also changed with different horses.
Nor does it address the fact that a horses back changes shape as the horse goes through its various gaits.
The Flexible tree used on saddles designed and made by James Saddlery not only have flex in the gullet, but through the entire tree. This means that when girthed up and with the rider on board, the tree auto adjusts to any shape horse or any shape the horse may change to, for example at the gallop as opposed to a walk.
It also can adjust in its length to allow for shoulder movement. It is evident that in a one leg forward position the horses back becomes uneven and out of square. The flex tree alters accordingly.
A change of gullet does allow a saddle to be used on different horses and that is great if the horse stood still and maintained that position it had where the saddle is fitted. The fact is that the instant your horse moves, it changes shape. A changeable gullet saddle does not change to suit. The flexible tree saddle designed by James Saddlery does change shape to suit various horses and the changing shapes of a horse in motion.
FLEXIBLE TREES GIVE YOU THE ULTIMATE IN SADDLE FIT AND THE SHOCK ABSORBING QUALITY OF THE TREE ENSURE SUPERIOR RIDER COMFORT AND MINIMISE THE CHANCE OF INJURY TO THE BACK OF A VALUED AND VALUABLE HORSE.