HD, different company now than 11 years ago. However having worked for both SERCO and NATS I know which is the better company!!
That said, I would never discourage anyone from leaving NATS and doing something different, working for a different ANSP provider is a good experience, and
can lead onto other jobs and helps you personally develop as both a controller and a person.
NATS tends to be very insolar in its thoughts and views.
Go for it.