Magic has nothing to do with this discussion of emissions. It's all science. When catalytic converters came out people were calling them an voodoo apparatus as well. Systems not using DEF and or DPF will be dealing with soot somehow, and in the case with EGR+CAT solutions that's done by way of pushing more exhaust/soot into the engine and into the CAT (CATs are what will, eventually, like DPFs, get clogged up and needing replacement). I'm NOT arguing for one over the other as I don't believe that there is really any "best" system (look at what the manufacturers of the most expensive equipment use- I know that in the automotive world you're looking at Benz, and Benz uses DPF and DEF); as an owner of VW TDIs (older ones) I followed the VW diesel fiasco in which VW skirted DPFs (and DEF) and ultimately got caught: is this going on with tractor manufacturers? maybe, maybe not; I doubt that they'll get scrutinized like VW was, not unless they're a top manufacturer and competitors are looking to slap them down.
OP, identify what capacities you need (loader lift; weight if you're you're going to be pulling dirt contact implements). How much time do you expect to be using this tractor? Think about ergonomics: shelling out a lot for a tractor I'd want to have it feel like it's worth the money I paid for it.
Buying used can have benefits other than a lower purchase price. Most manufacturing problems/issues will likely have been worked out. And, initial maintenance costs (early fluid changes etc.) will have already been dealt with.
Unless a tractor has been totally abused (and even then!), it's likely able to rack up thousands of hours. How many hours do you expect to put on it? (my
B7800 was purchased with 748 hrs on it and I've now put on an additional 750+hrs and it still is a reliable, mighty little workhorse).
Buy what makes sense to you. Work your numbers. In the end, however, most here aren't going to have true payback (unless you're running a business and have the equipment on a depreciation schedule).
