Been told these are indeed legit, however these free top up deals are for selectives only
"It's top-up treat time: Top up £10 and we'll give you a £10 Everything Pack for FREE! You'll get 150 minutes, unlimited texts & 500MB data to use in 30 days. Just reply YES before midnight Monday 19 Dec then top up £10 to get started. Terms: http://discover.ee.co.uk/loyalty/xKMhMX
Text STOP to 2000 to opt out from marketing."