I don't really like this name, as an idea... maybe if it was on a person and I could see what it feels like to call someone Cristyn, I might like it better.
I have never heard of this name before, and I find it highly unlikely that a Welsh person would use it since it's so similar to the Welsh word for 'crust' (like you get on bread, or pizza) which is 'crystun'. Who'd want to be called 'Crust'?!