I agree with Ali B totally. Much though i enjoyed RAF life, the niff-naff and trivia associated with a commision these days has definitely taken the shine off it. NATS will only credit you with the NAV training and excuse you from one [piss-easy] exam at the college.
If you want to join NATS, join now. If you want to wear the blue suit, then go in for the right reasons and do something you will enjoy. I found WSO wasn't for me so handed back my green baby-gro and went to Hurn. The raise in salary and lack of secondary duties made NATS a better life straight away. The fact that ATC is a bloody good job filled with bloody good people is the icing on the cake.
If you are not in it for the long haul, you'll pretty soon lose the respect and support of those around you.