Bastard Bios are awesome, no problems.
Keep in mind though, bio bbs start to degrade when exposed to moisture and light, so make sure to keep them in a dark, dry place after you open the bag, and try not to let them sit too long.
Also, systems with really tight tolerances like systema stuff and precision tightbores will like them a lot less than most other guns, and yes, if your bbs are old and degraded they will fuck shit up.
However, if you're running a crappy to good quality AEG and follow standard maintenance procedures every few games, there's absolutely nothing wrong with bios, as long as they're good ones.
Bastards are good ones.