The 3350 doesn't have a traditional DPF, and the issue isn't only that it "regens" a lot... It's that the tractor becomes basically unuseable due to numerous regen issues. To my understanding.
Which is why dealers still have NEW ones from years past, that they won't sell... They are that bad! Very well known lemon. I'd run from that tractor. Probably one of the most famous Kubota tractors of all time