This is an explanation I wrote not too long ago for someone else. Forgive me if the tone is a bit defensive they weren't nearly as polite as you. Cheers m8!
ModMii does NOT install an unofficial priiloader. An older version of the OFFICIAL priiloader is installed using a modified installer, but what actually gets installed to the console is the same as the official installer. The modified installer uses IOS236 instead of AHBPROT because when ahbprot support was first released by the Homebrew Channel (HBC) there was a network initialization bug that would cause loaded apps to crash if there was no wifi connection saved to the console. As you can imagine, if this crashed in the middle of a priiloader installation then it could lead to a brick situation. At the time wii.guide did not exist, but similar reputable guides (including ModMii) ALL used the 236 installer mod. The latest version of priiloader and other apps have solved this network init bug (or last I researched it the solution should work in 99.99% of cases). I am hesitant to switch over to using ahbprot because of the 0.01% chance of brick as I want to maintain ModMii’s reputation as never having bricked a single console. The version of priiloader that ModMii uses has been much more thoroughly tested than later versions of priiloader (in part because of ModMii’s popularity). I have always been reluctant to switch to using a newer version of priiloader since it impacts the system menu and can result in brick if something goes wrong. You may recall a number of bricks occurring from a buggy priiloader release a few years back. DacoTaco hates when I bring this up, but the fact remains that a number of consoles were bricked from older priiloader installations. He has since fixed the issues and continued his amazing work, but the fact remains that upgrading to untested versions of priiloader is not a good strategy (especially for consoles who cannot install bootmii to boot2 for ultimate brick protection). The latest final priiloader release doesn’t offer any significant improvements over the version used by ModMii so I prefer retaining the tried, tested and true version used by ModMii (if it ain’t broke, don’t fix it!). Now the latest BETA version of priiloader looks promising as it has added a number of new features and improvements that would make the switch worthwhile (i.e. support to navigate the menu without a controller using the buttons on the console itself, better loading of installed files, gamecube controller support, keyboard support, etc.). I am waiting for it to move out of the beta stage and become final, and for it to go through a reasonable amount of testing for me to be comfortable it is safe before incorporating it into ModMii. In short, only this most recent beta version has improvements compelling enough to migrate away from a more thoroughly tested release, and ModMii will switch to the latest version when it is FINAL, and not before.