First off.......
The firmware change is not supported or acknowledged by Canon in any way shape or form, if the installation goes wrong it can kill the camera.
That said, i've not read of any failed installs and i'm pretty sure you could attempt to reboot it again with official firmware.
The altered firmware brings a few other handy features, from what i've read you'll gain ISO 3200 and mirror lock up along with flash exposure compensation.
if your going to try it, download the current canon firmware and keep it safe, and make sure you follow the install instructions to the letter.
The site where the download comes from has full instructions as well as a list of features and how to access them using the new button press sequences.