Flat cutback saddle equitation arabian HELP?!?

I found a saddle and it is called an "Crosby Cut Back Equitation Arabian Saddle 21" I know crosby's are good but do you think that would fit a Half arabian well? and i don't know much about saddles besides brands and comfyness how much would you think this saddle is worth if it was only used 2 times! and would a 21 inch flat saddle be good for a person who is usually a 17" hunt saddle (im not worried about it being too big HELP now please!