No, its not total nonsense.
It is not uncommon practice in employment contracts in other professions, its just that in aviation we generally see the financial training bond instead.
Its not unreasonable that company A should consider that the skills gained at its expense should not be used to benefit its competitor. I would say its a lot more moral than a training bond, because if you leave you are no worse of than you were before, and you would be accepting the training on the basis of serving the term of the contract.
pb