The bond has recently come under scrutiny from HMRC, affecting at least one airline. Be careful as it may not be available down the line. Be under no illusion you're not sponsored and you pay the full price for the course. The "bond" is just a tax advantage for the individual. If you are based outside of the UK then you cannot claim the tax advantage.
It certainly used to be able to be transferred between participating airlines and I know of several people who have worked for 2 carriers, both repaying the "bond"