There's no reason to stay on 5.5.1 anymore. I think it's better to go to 5.5.3 right away and forget about the problems you'll have if you stay on 5.5.1 (game update not working, game launching giving an error, no eshop access, CBHC removed after updating to 5.5.3). Even if it's entirely possible to stay on 5.5.1 version and fully hack the console, it had some disadvantages: It required more steps and tools to hack it, and at the end you'd had more issues staying on a lower firmware. This guide used to cover multiple firmware version (5.5.1, 5.5.2 and 5.5.3), but I decided to drop support for hacking the Wii U on lower firmware.
Last updated (added new stable web exploit for 5.5.2-5.5.3)
