Promissory Notes are a form of legal contract to make payment and is covered by the same legislation as that for Bills of Exchange and Cheques.
A promissory note offers less protection to the payer than a cheque would.
e.g. if you purchase an item which you never receive, you can legally cancel a cheque to stop payment, however payment on the promissory note must be made on the due date whether you received the item or not.