I‘m sure as someone said, some may be better, some likely worse. I don’t question it. The savings I may get by buying another brand is not worth it if it fails and I have to pay for an engine or new tractor.
I know Kubota doesn‘t make filters or oil. However, if they put their name on either it meets their specs and I don’t have to worry whether it is “good enough”. Some here swear by other oils and I have no issues with their choices. If I’m stopping at a dealer for the filter might as well get the oil, too.
I know some of you don’t have convenient dealers. I‘m fortunate in that I pass 3 Kubota dealers on the way from my home to my land. You can order it if shipping doesn’t outweigh gas to travel to a dealer.
By the way, the filter and oil I replaced yesterday as part of my maintenance on my L2501 were both branded Kubota.