But before I waste £40 on a Hive Crone as my anti-air option I thought to double check.
I've played a Nid player with a Crone a few times; we sort of ended up with the notion that to have truly effective AA, you needed 2 Crones. One Crone shooting 2 Tentaclid Haywire Missiles (with a 75% chance to hit, thanks to the rerolling BS3 against flyers) is only likely to put 2 glances on a flyer, not kill it outright, and one Crone doesn't have the threat radius to be able to Vector Strike a flyer against a canny opponent--they can alway bring on their flyer on the other board edge, or something.
2 Crones, on the other hand, get 4 Haywire shots (likely 3 hits, so about 3 glances or forcing the opponent to Jink), which will incapacitate a flyer pretty well--and should be able to split up and be able to Vector Strike something that comes on.
These are just my observations, mind. The change to the number of hits against ground troops that Vector Strike can net you is disappointing for the Crone's damage output, seeing as 1 S8 hit somewhat less remarkable than D3+1 S8 hits, even if you still have your fancy flamer.