The function approve is vulnerable to the front-running. This issue is described here: https://blog.smartdec.net/erc20-approve-issue-in-simple-words-a41aaf47bca6. A malicious delegate can scout for a change in approval and front-run that. It is more of a theoretical issue, but still, I want you to be aware of this and that.
Recommend introducing increaseAllowance / decreaseAllowance functions.
albertocuestacanada (Yield) disputed: see here for full explanation.
