I don't think I would buy the Riptide a Velocity Tracker. It doesn't have the right kind of shooting to do much to flyers, it's good against ground targets because big scary template, but against Flyers you'll only be firing three S7 shots and one or two S6 shots at BS3 which just isn't likely to accomplish much and is a waste of the damage it can deal against heavy infantry with the S8 AP2 large blast.

The Broadsides should take care of anti-air just fine by themselves, that's a lot more S7 shots and re-rolls to hit.