Kubota doesn't manufacture their a/c compressors, so if you can find the original manufacturer and buy an identical replacement at a saving, it makes sense to go "aftermarket". You don't want to use an unknown air conditioning compressor since it is a difficult job to start with and if the inexpensive compressor fails you get to do it all over again.
Air conditioning repair is best left to the people who have both the tools and the knowledge to repair it properly the first time, and keep in mind that even if you know but not the tools getting those tools is going to be expensive for a one-time job. I have the tools and the knowledge, and I still don't do air conditioning work on my vehicles other than the antiques. Modern air conditioning units have far too many changes than I learned 50+ years ago. I don't understand why Kubota tractors have so many air conditioning compressor failures other than using an inferior product. It reminds me of the air conditioning compressor failures that Mercedes was using in the mid-1980s. Before that, they were using the GM A-6 compressor that was bulletproof.