Localized growth is how people see it for themselves. Of course your bi is growing to grow when injecting into it. It is swelling from a substance being put in a place that has no room. And the BA cause irratation at the site which causes swelling. Does it work?? There is no proof that it should do any better, except with short ester ASes which was posted before. But this is still unclear.
As far as pain. You bi or tri should be sore the day you inject and usually the day after. Then it goes away. If you tend to work out after the injection then the pain is not as bad, for me at least.
Should you inject before or after you work out?? Before.....after you work out you muscle is pumped and go pushing a needle in there while the muscle is still flexed, and you will know pain.