OK, James, I installed the springs into my friend's Diggit EM15, and we both like the improved feel. Adding more resistance to the the joystick motions is a plus. Worth trying, IMO.
Here are some pix. The install is very easy, but there are issues with how this joystick is made. The inner boot has is too thick to fit in its upper groove, so it was loose. You can see damage where the installer tried to force it in. The outer boot really needs a plate to secure it, and keep the mounting bolts tight. There aren't even washers there.
The spools should be greased, and the inner U-joint needs some thick oil. That was done here (photo).