Absolutely the bestest thing I ever did for my horses (and indeed my own back) - I have the Freestyle (gulleted dressage model) and the Jumper. Nearly had to remortgage the house, but well worth it. Have nearly sold all my old saddles now anyway, so recouped some of the money that way.
It took me two years from first trying one to actually take the plunge and buy one, and I wish I'd done it sooner. The difference in my horses was immediate, and one in particular who used to be really tense and spooky has completely changed, and muscled up through his neck and trunk, where he was very weak.
They take a bit of getting used to, as they sit you quite wide, but they are very comfy (treed saddles feel weird afterwards). It is really important to get someone to help you fit the saddle to the horse, and the saddle to you (blocks, columns etc) - I know some people give up because it hasn't been tweaked right for them - once you've got it right, you just whack it on and off you go! The impression you get is that one saddle fits all, which it does, but only once you have sorted out the shims, wedges, type of pad or numnah etc. Ultimately, once the horse has changed shape, you should be able to use the saddle on say a polypad and nothing else.