The major advantage I see with this over HipChat is that you can use existing IRC client software to connect. Personally, I'd much prefer Irssi in a terminal to an Adobe AIR product.
You can connect to HipChat from any Jabber client, though unfortunately it makes chat rooms slightly less discoverable. (I’ve used Adium with reasonable success.) The big advantage is that (at least on a Mac) the Adobe AIR version is a tremendous CPU hog.
I can see the reasons for that, but the HipChat application lets you drag and drop files to share them with everyone in a room, auto-loads images... that alone is worth the client app to me.