The "Brick Risk" with the Homebrew Channel ultimately depends on how much modification you're planning on doing.
Installing the Homebrew Channel itself is very safe as it has an extremely low "Brick Risk" (only a power outage during installation can cause problems).
Using basic homebrew applications is very safe as it doesn't tamper with the Wii's internal memory.
Using advanced homebrew applications that tamper with the Wii's internal memory (Trucha Bug, cIOS's, ect.) is probably the stuff you want to avoid as your "Brick Risk" increased considerably with these.
If you want to install the Homebrew Channel & you're running Wii menu 4.2 or lower, here's the suggested method.
1) Install the Homebrew Channel using the Bannerbomb exploit.
2) Upgrade your Wii to version 4.3
3) RE-INSTALL the Homebrew Channel THROUGH the Homebrew Channel -- This re-installation will have the Homebrew Channel use IOS 58 (which has USB 2.0 support, included with Wii menu 4.3) instead of IOS 61.
Just be aware that once you've modified your Wii with the Homebrew Channel, you'll want to avoid upgrading the Wii Menu until the developers of the Homebrew Channel have released an "Wii menu safe" update... For example, when Wii Menu 4.3 was released, it was detecting the Homebrew Channel version 1.0.6 & lower... It took about a month for version 1.0.7 to be released (& later version 1.0.8) to circumvent the new detection measures.
So when the next Wii Menu update comes up... wait for the next version of the Homebrew Channel to be released before you consider updating your Wii.