I love this prefpane.
It provide a fast, reliable, uncluttered, intuitive way to change my User Agent. I can add my own presets and delete shipped presets, all very quickly. Also, when setting back to the default User Agent, it actually gets rid of the override, instead of just setting the override to the correct user agent. For added spice, it even picks up the icons (even custom changed) of all the presets (even ones I make). :)
I'm a happy website tester today.