I have the Fairfax World Class models for both of my youngsters as their first saddle (one is 3 now and just under saddle; the other is 5). I love the saddle for myself and do consider this to be a long term saddle as long as it continues to fit my horses. I love the narrow twist on it and the prolite and the adjustability. It’s not a cheap saddle.
My older horse likes the monoflap design without the lower knee blocks (just the blanks) because he has very wide shoulders; the younger one, who is more narrow, goes with the medium knee blocks. I also keep a saddle fitter pad, just because they can change so quickly, but I do get fittings by my independent saddle fitter about 3-4 times a year at this point. It seems to fit a variety of horse very well, and Fairfax has a lot of seat/flap/block options for this type of saddle. I had another model initially, but I did not like the thigh block placement for me or the twist. I worked with a fitter who would work with any type of saddle, but did rep Fairfax and some other brands and so she was very familiar with the saddle and how to fit it.
I did try A LOT of saddles when fitting the older horse when he was four, and even had a custom saddle made for him (that ended up being too wide for him). I sent A LOT of saddles back. I think with the young horses, it is very difficult to fit them long distance and that is what happened with my custom saddle.