Well, I got my ZB2520HL and I'm happy to report that all JST connectors I have put through an out-of-the-box lead-free temperature profile came out just fine without decolorization. Same for crystals and electrolytic caps that sit on a a plastic base.
Now, that said, I have noticed a particular change. The oven now comes with a glass fibre mat that sits in the drawer. My guess is, that the IR now does not reflect from the polished metal, but rather heats up the entire drawer surface, creating a more even heat. Since this oven also has a fan, that yields a very even heat distribution.
I am doing more testing, but so far I can recommend the ZB. It's a significant improvement over the T962. It comes with proper earth connection to the chassis, and does not include materials that try to poison you the first time you fire it up.
The menu is a bit wonky, but usable. There were some minor cosmetic issues. The from decal was loose in a corner and the laser left some sputter that could have been cleaned up. I will start a separate thread with a brief review.