While this approach should work in theory, in practice some web sites will reject + as an invalid character for an email address. They are incorrect, but that won't help you with entering such an address into their incorrectly-programmed site :-/ And even if they allow you to input it, + is a special character for URLs so depending on where/how the site passes the email address around there is potential for bugs to occur there also. (And not just saying this as a hypothetical, I have run into sites that have both of these issues)

Bottom line, I would recommend the . approach over the + approach when possible.