Julie from Migration Downunder prepared my application to move my 457 visa to a new sponsor. She was upfront that the approval could take a few weeks because it was a busy time, but in the end it went through in less than three. She was very friendly, quick and responsive, and was happy to also answer some questions about the permanent visa I'm planning to apply for.
My employer paid for the service (which is normal) so I can't rate the value, but I'd recommend Migration Downunder for fast and effective preparation of applications.