[MadMax]

I haven't done actual measurements of sphericity or group size with softair branded bbs, but I can reasonably state that bb quality does matter to some degree.

There are some brands of discount bbs with consistency issues. Very cheap bbs can include very obround pellets which can jam in a barrel and cause serious loading issues. Some brands of bbs are soft and may break in electric loaders jamming them to the point of stripping gears. Not every pellet has to be so bad that it would jam a gun or loader. One pellet in 500 pretty much renders a bag useless if you find yourself having to clear a jammed barrel. One pellet a bag which would strip your autoloader gears would have you cursing soft ammo which just destroyed your $60 loader.

A bb has a pretty small clearance between the diameter of the pellet and the inner diameter of a barrel. Very poor surface finish (i.e. unpolished seams or mould mismatching) can result in inconsistent performance.

Apart from grossly poor sphericity (i.e. jamming) it seems that small amounts of obroundness don't hurt consistency all that much. Weight plays a larger role in consistency than ultra sphericity in windless range tests. I haven't bothered to test bbs with severe seam lines as they tend to jam my guns, but I would suspect that heavy seams could significantly affect hop up consistency as the rubber would grip a seam quite differently than a smooth spot. The spin direction with respect to the seam axis would also likely have some significant effect. For instance, Straight brand sniper bbs are very consistent in range tests, but they are nearly the worst in terms of measured sphericity. I suppose outright mass (0.36g or 0.43g) plays the major part in making sniper weight bbs consistent flyers.

Getting to an airsoft game is at least a small ordeal for most players. Throw in saving money for a limited arsenal and most players are quite willing to spend a chunk more for consistent ammo. It's kind of like war really. If you don't want to spend a lot of money on ammo which doesn't misfire or sometimes fragment, you can buy lots of cheap bullets which sometimes spin out or misfire. Generally you'll still have quite a deadly weapon, you'll just have ammo that could really frustrate you in a bad time. If saving on bbs can put gas into your tank to get to a game, you don't really have a choice anyways so buy the cheap stuff.