What is the difference between cheap and high-quality BBs? There can be quite a bit when you look up close.
Here is a sample of a Marui 0.20g BB and a no-name brand. Judge for yourself.

This is a cheap noname BB. It’s unlubricated, but I fixed that by spraying some Silicone lube into the bag and shaking them up. But that still doesn’t address the other issues. Click on the image for a closer look. You should be able to see both mold lines as well as flash (extra bits of plastic from a ‘leaky’ mold).
At best, the roughness will affect your accuracy. At worst, the BB will jam in your gun and increase wear on your gun’s internals.

Here’s a Marui BB. Marui and Excel are considered by many to be some of the highest quality out there. They are lubricated with silicone and the manufacturing is top notch. It looks and feels like a slick, brand-new miniature cue ball.
For best results in any gun, it’s best to ditch the cheap junk and stick with good quality BBs. This is particularly true for some of the higher-end guns that can be fussy. For example, my TM Mark 23 tends to jam up somewhat on some of the cheaper brands of ammo.