I printed the concave version in PLA and ran into the same issues as @Mashiem. The nibs and the edges of the legs were a bit too sharp, but some sandpaper took care of that without too much effort. One of the legs broke off for me, too, but I found that it actually slides on the joystick pretty nicely with three of the four legs, so I just trimmed off the rest of the broken nub and kept using it. I just posted a make, if you're curious to see what it looks like.
The biggest issue though is that it looks like the legs keep the joystick from tilting all the way. Might be good to modify it so they don't extend quite as far past the bottom of the stick.