S6 helps against other dakka jets (he who comes off reserve first loses a flyer!), but a necron flyer list is going to be more flyers than you can bring down before getting brought down, and the other scary flyers are AV12 (which S6 just isn't very effective against). Lootas might be better - they're only half as effective against air targets as they are ground targets, but that's still better than most alternatives. I'm not sure how that works out for FOC or points though.

I think the dakka jet is fine, I'd just be leery about how vulnerable it is without more than one.