There's no argument for or against it's all down to your own opinion.
Vote Yes if you think in the current climate it's a fair offer and you are happy with it.
Vote Yes if you think it's the best offer that can be got through negotiation alone and either aren't prepared to take industrial action, think that industrial action won't improve the offer or think that your job might be at risk if industrial action or a bigger payrise will result in NATS needing to save more money than it currently suggests.
Vote No if you think the offer is too poor to consider.
Vote No if you think there is better to be had by either the threat of industrial action or actual industrial action and, most importantly, you are prepared to take that action.
Don't vote if you really want to upset some of the people on this forum
, although personally I think it's perfectly valid not to vote if you really can't decide which way to vote