I'm a little unclear if the OPs offer differs from Kafra's? From what op wrote it seemed his was valid for his flight today, whereas Kafra's is open for any travel between those dates.
I havent had an email, and I have a flight coming up on the 21st from LGW, and I actually have 3 friends on the same flight, so it would be handy, not unbelievably, because we're all in CE, but nice.
Last year with the same offer, there wasn't an issue at all in the LGW lounge, hardly anyone there at all.