Hmm... I'm guessing they're the same Egg I had a card with years ago (late 1990s) in the UK - surely there can't be more than one CCC called Egg out there!?
If it is the same company... the card I had was pretty good, high CL, zero percent introductory rate, etc etc etc - Egg was a very popular card at the time. They were part of Prudential - I just Googled to see if that's still the case and it turns out they've now been bought by Citi, which might explain why (if indeed it is them) they're sending out offers in the US now.
Word of warning, though... they were in the news a few months back for, if I remember right, reducing CLs and cancelling cards all over the place. Egg claimed they were carrying out this action against 'high risk' customers... only for there to be a flood of outrage from CLD'd customers who never carried a balance, had never been overlimit, etc etc - ie the unprofitable ones! (See
here, for example).