Firstly, I am not an ATCO (yet?)
I think you have answered your own questions to be honest. Any job is very personal to the person considering it, and you appear to have identified the "cons" as far as the job would affect you.
If you don't want to be talked out of it, then don't let it affect you, but don't bury your head either.
Even the strongest personalities with the best job in the world can fall to depression if the environment isn't comefortable for them. Is it worth getting depressed for a pay packet, and a chance to talk to Aircraft? - That's for you to answer I suppose.
I would say that any job has draw-backs, and NATS appears to be a place with just as many as any other. It's just the "Pros" of the job seem so over-powering!
A few Cons I've noticed by reading these forums:
Terms and Conditions - It seems as though NATS management is quite happy to provide pretty bad T&Cs for its employees.
Shift Working - A Con you feel will really affect you.
Mobility - You have to be able and willing to move anywhere in the United Kindgom, at the say-so of the company. That's a big ask for anyone who isn't a single person.
Training Pay - For a 27 year old, the pay during the NATS training is likely to be significantly less than that in your current job. Of course, there is no guarantee that one will pass the course either!
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As you said, you know the pros so I won;t list them so far as I see them, but I should at least note that, in my opinion.. the Pros out-weigh the Cons to such a degree that job satisfaction of many other options open to me can't even be compared.
Phil
P.S. I say again, I'm not a NATS employee (yet) but I'd like to be! :P