Knowles and Sonion drivers are supposed to be of better quality for BA drivers and were usually found in more expensive IEMs compared to the usual cheaper Bellsing drivers we find in cheaper CHIFI like KZs.
Though ironically, the cat is out of the bag that some TOTL IEM brands use Bellsings (
https://www.reddit.com/r/headphones/comments/cxqlje/knowles_files_claim_with_us_trade_commission_to/), whereas some CHIFI companies use Knowles and Sonions in their IEMs. Knowles alleges Bellsing copied their stuff, so there's a big lawsuit going on in US now in the above link.
Personally, I find Knowles are less harsh and have a less artificial timbre than the Bellsings in general, but some people find the Knowles sounds too "clean". Though as u can see, even TOTL sets use Bellsings and not many users are complaining that the sound is "off". I think the Bellsings are catching up very fast to the Knowles, and are cheaper. In fact these cheaper drivers helped to get us cheaper CHIFI products for good sound quality the past 2 - 3 years, though it is a big can of worms on the ethics of it.