This is real I'm on the trial recieved my BT sim couple weeks ago. Working pretty well at the moment although had emails to say they're having issues with activation and number porting at the moment. Speeds are quick but like above it is using the EE network. As a trialist your given 500 minutes 1gb of data, 1000 texts and unlimited wifi but they're encouraging you to use more (everything even over spend is free) and looking for people who travel abroad a lot to take part in the trial.
No mention of tethering on the trial and haven't used tethering yet to see if it's allowed.