When the guy sitting in the seat contracts lung cancer he/she is not gking to be impressed by that 3% number. Particulate mattet in diesel exhaust is a human carcinogen and just like cigarette smoke inhaling it is bad Ju-Ju. The more we do to reduce operator exposure the better.
I don't have a DPF on my L2501. I decided I'd get by a bit less power. But, I've been bit by a fault DPF emissions system on a truck. It really stinks to go into limp mode when you try to go up a mountain. If I needed a high HP tractor, I'd go the DPF/DEF route. It seems like they've been fairly reliable. Fwiw, I don't think I've ever smelled my exhaust under way, but I've smelled cigarettes.
Lots of things cause cancer. Newer research implies diet is a big contributor for cancer. They still sell most of those foods. Any way ...
In any case, people modify emissions systems due to reliability issues. I think the problem is and we saw this with B3350, engineers have a hard time matching how people use their tractors compared to how they are really used. I'm not picking on tractors or Kubota though. Trucks have the same issues. I was watching an interview with Gale Banks the other day and he was explaining why they produce engines for the military etc. The main reason was reliability and the ability to use "any" diesel fuel the world over.
A little better job by engineers in the beginning and nobody would have bothered to find solutions to delete emissions on trucks/tractors. That's an engineering and govt issue. In Canada, they don't have a nation wide rule ... it's by province. There are real reasons to delete unfortunately.