What is the difference between BootMii and Boot2

Exactly as the titles says, what exactly is the difference or is ti the same thing?

Boot 2 is a piece of software, written by nintendo, that is part of a few programs that boot the wii. Bootmii, is piece of software written by team twiizers, which has two versions. The boot 2 version is made to replace nintendo's boot 2 software. This allows many things for homebrew most important of which is the ability to backup and replace all of your data in case of a brick. The other version of Bootmii, the IOS version, is the same program as the boot 2 version, but because it must be loaded by the rest of the system, it doesn't allow for the same brick protection. If you have a recent wii, you can't install the boot 2 version, and you are stuck with only the IOS version. The hackmii installer from which you install the homebrew channel will tell you of you can install the boot 2 version.

I see.

So I may or may not actaully need the Hackmii Boot2 with my 4.3U but it could help in case my Wii gets bricked? I want avoid that risk and just want to make sure I don't brick my wii.

You shouldn't have to worry about bricking your wii unless you start downloading a bunch of dangerous software, most of which is not allowed to be discussed here(Backup loaders, etc). The rest of thr dangerous software is clearly marked. As a general rule, if you don't know what it does, don't use it. If all you want to do is play homebrew games, and watch movies, you have nothing to worry about.