I have run one on one of our Banshee's for three seasons now, I would expect it to outlive the rest of the quad. If you wreck bad enough to bend an aftermarket axle, the rest of the machine won't likely be salvageable. As far as the splines, the quality and fit are good.
For the 3mil crank you will need to buy seals, gaskets and either re-use your crank bearings or replace them. You can either run a spacer setup or have your head milled and rechambered for the additional stroke. I recommend portwork to match the increased stroke to get the full bennefit of it.