It works 95% of the time, but be aware that it sometimes doesn't:
- Some webpages refuse addresses with a + in it.
- I’ve had at least one instance where I lost an important email because I could register and receive emails from them, but one of their internal databases silently failed on my address. (I lost the proofs for a paper accepted in a journal, and it took some time to figure out what was going on…)
- There was at least one web page that was smart enough to just remove the +… from my address after I registered.
- Some webpages require you to be able to send emails to them from the exact address you sign up with (including the +…)
Overall I’ve been happy with the feature since it makes e-mail sorting easier, and you can just redirect a given subaddress to spam if they leak it, and it’s less effort than creating a “real” email alias per page. Just keep in mind that there are many ways it can fail, so you might not want to use it for anything that is actually important.