Maestro used to be Switch. They were popular at one time for under 18 year olds for some reason. AMEX is really seen as a premium option here in the UK, for travellers and those with rich blood.
Maestro is in effect a card network, the under 18 popularity stemmed from having a line of cards that were low transactionality, it was the first issuer in the UK to really give cards to under 18's.