I would not give blanket advice to sign the undertaking without knowing the full picture. I can't give legal advice in a forum. I have simply explained why these undertakings are issued by employers.
Can I take it from that non-answer of my question 'are you a lawyer?' that you are not a lawyer? Typically recruitment agents and HR people are not. (But of course they have access to lawyers and some relevant training and experience.)
There have been countless occasions where I have advised against signing and similarly there are cases where I have advised to sign. Likewise, there have been cases where an employer attempts to push the ex employee to sign because they realised there is no confidentiality clause in their badly drafted contract (often downloaded from rip off websites). In those cases I would send a very blunt letter advising the former employer that the only way of getting the employee to agree to a new restriction would be by way of a settlement agreement with appropriate payment.
Thank you, that's a fair answer.
But what we're all struggling with here is finding any circumstances where an employee would benefit by signing such a deed. A simple reminder of the confidentiality terms of the contract is all that is necessary, anything more has the nature of a threat and is not in the employees interest.