That rust is on the adjusting nut, not the sealed bearing. You could replace them with a SS nuts of the correct thread if you wanted.
I'm running all three megan arms on mine DD, track, and heavily salted winter with zero issues. Is it the best? No idea as I haven't tried anything else, but I'm also not experiencing any noises or slop. FWIW and YMMV.
Disclaimer: pic from when freshly installed:
