Doing an A/B with all BA sets using Knowles versus Bellsings, what immediately strikes me is that the Knowles signature sound is somewhat smoother and cleaner. More rounded and less harsh than Bellsings. In general, timbre for acoustic instruments is slightly better on Knowles, but won't be as legit as pure DD setups.
Well this is just subjective, as the above areas can't be measured, and I've audiophile friends who like Bellsings more than Knowles. In fact in terms of technicalities, sometimes I find Bellsings are clearer in details than Knowles, so maybe it is not the driver brand but the implementation and tuning that is of more importance.
Whatever the case, Knowles is in the midst of a lawsuit against Bellsing for alleged copying:
https://www.reddit.com/r/headphones/comments/cxqlje/knowles_files_claim_with_us_trade_commission_to/
Probably the coronavirus is delaying the lawsuit proceedings, but it seems a few TOTL companies even use Bellsings in their gear according to this lawsuit, so their audio engineers must recognize that Bellsings ain't too shabby (though saving costs by using Bellsings is probably another factor).
Morals aside, Bellsing is one of the reasons why we can get such affordable multi driver BA/hybrids the past few years in CHIFI. Previously a multi BA Westone would be costing upwards of $250, a single BA Westone would be $100 at least.