It's been made clear to you a 457 visa is risky. If you are willing to take the risk go for it! I know a person who have come over on a student visa to train as a Chef, then got sponsored on a 457 and is now permanent (actually a citizen!) So with a bit of luck it can work out for you. Unfortunately I also know a lady who feels trapped in her job on a 457, due to her working conditions and personality clash and a family that had to move back to the UK, with the family being devastated.
You know the risks, good luck to you!