Just got my 3 cars today and thought I’d share initial thoughts. I will post a YouTube comparison this weekend.
Paint is fantastic and crisp. Lionel kept the same trucks which roll great. The paint on the door hinges does not flake, I must have opened and shut them all 20 times to be sure. The coupler is fixed (no side to side movement) just like the 2020 cars and unlike the older versions, I was hoping they’d fix this but they did not. The coupler itself IS different from 2020 versions in that it’s narrower, has a small piece on the end almost like a spacer, and DOES couple with older Lionel milk cars. It’s not a perfect fix as these 2021 cars won’t couple on my 0-72 curves and sometimes takes several tries even on straight sections. They don’t appear to derail as easily but I need to run them through some curved switches. Ironically, they don’t couple with the 2020 cars but it sounds like new couplers will be issued for those. Overall not perfect but much much better.
The cars are beautiful. I received my Renken milk car a few days ago. Like you, however, I was disappointed that the couplers are not articulated, so I won't buy any more of the new milk cars. I am not worried about derailments with my new milk car, as my curves are all O72 or larger, and I will also place the Renken car between two of the old Lionel milk cars that have articulated couplers.
Hopefully, Lionel will go back to installing articulated couplers for all of its freight cars in the very near future. I still don't understand why they downgraded their couplers by making them fixed. I'm planning to speak to Ryan about this issue at the York Meet.