A search on this topic will turn up a lot.
That said, at least in the case of the HST filter, for those so equipped with a magnet, NONE of the aftermarket filters have this, therefore, regardless if the filter is listed by a aftermarket filter maker as being the same as oem, it is in fact, NOT.
In this particular case, it can be said that the aftermarket filter makers are outright lying to you if they have a filter that "interchanges" and if they are willing to lie, what else are they doing to make there filters cheaper than the oem.
Yes, Kubota does not make there filters, but the filters that they have produced are built to Kubota specs. And that in no way means that the next batch of filters coming down the line for Fram (just for example) even though they "cross" over, are the built to the same specs.
It is hard to find EXACT specs on filters, when was the last time that you saw a specification for total filtration media? Fuel filters generally have a micon size filtration, but have you ever seen that listed for a oil filter? Unlike oil where everything is spec'd out.
and then there is the whole false economy thing, so you save $3-$4 a filter, what than means you save $30-$40 over a thousand operating hours for lube oil filters, of unknown specifications I might add. Not much real savings there in my opinion, after all those filters are protecting a 5k engine, and by extension a 20k tractor.
Food for thought
David