it's noted that Z4 only works with Froyo.
With GB the methods are different. It's perfectly ok if you want to run Froyo just make sure you're flashing a Froyo rom on it and not a GB rom. The only problem is Froyo roms will be severely out of date.
I used to be Android all the way but bought an Iphone 5 in October. Feel free to ask me how it's going via PM.
GO BRONCOS AND ROLLLLLLL TIDE!!!