Estyn is a real name. It is a derivation of Iestyn but definitely a real name. (I was on the phone to one bout 2 hours ago!) There are 10 Estyns registered to vote in the UK. Interestingly 2 are Estyn Williams, 2 are Estyn Jones.
One snag with the name is that people often instinctively think it is a female. Another is that it cannot be given without the word "what" being said afterwards.