treeless saddles feel very different to ride in to begin with, your legs feel like they are being pulled back! once you get used to them they are comfrtable but i find that they make my backache if i ride in one for more than 2 hours! they are very light and horses seem to go well in them. the accesories are expensive tho because you must have the special equitex saddle pad which costs £80! and you need special stirrups as there is no safety release at the top of the saddle! so stirrups such as the barnes buckle or toe hoods. you also need a dressage girth. the saddles also tend to slip more than normal saddles.
i think you should borrow one from your saddlers and definately try one before you buy one!