XL has many more ball bearings in the head. it's got very little slop, longer blades, longer tail, and many parts are improved either in material, design, execution, etc. the tail rotor system is forked which is very precise. it's a LOT better than the old one. production is already stopped on all non XL except SE. if you want something better than a 450X but cant afford the XL buy an x400.