This is a really fun trip to do and it's marginally cheaper than booking the ferry and the bus trip on Rottnest Island separately on their own. Although do note that a) the bus trip doesn't let you off anywhere. If you want that option, get the hop on, hop off bus. On this bus tour though you do get some excellent commentary, and b) once the bus tour is done after about 1 3/4 - 2 hours, you're left to your own devices.