I think you may be asking for too much--an evidence-based acoustic or engineering purpose for a particular feature.
Perhaps Yany's prototype testing guided their choice, but equally plausibly it is all marketing-based and they believe they can sell more or charge more or both by including metal resonators in the TWO-20.
How about you, OP? Do you think metal resonators add value to a particular model?
For me, aside from the resonators and ignoring the price differential, the TWO-20 has many, many small upgrades in the design of key feet and soft materials and mechanics compared to the -02 which are completely aside from the marketed Pro vs. Elite features. I had been led to believe the TWO-02UL (posts vs. ribs) would be lighter--important to me--but in fact they were the same mass. With both in hand for direct comparison, the -20 seemed clearly even more exquisitely engineered and constructed than the very fine -02.
I'm not at all diminishing the TWO-02. It sounds fantastic and is an amazing bargain for the price. Many folks would not notice nor care about the small things that differentiate a -20, particularly if they sounded and played the same. But they are clearly present, and if they matter to you, you might pay the upcharge for them.