Not to concerned about it dissolving overtime as long as it is safe. I have also been doing research on this and learning all this for the very first time. I find this very interesting and wondered about getting a 3D printer. Here on this website "Is 3D Printed PLA, ABS & PETG Safe for Fish or Aquariums? "they talk about safe PLA plastic filaments and here is one pointed out on amazon HATCHBOX PLA 3D Printer Filament.I google searched "is PLA safe for aquariums" and perused a few articles about it. The consensus seems to be that it's OK in fresh water and won't kill your fish, but I'd probably do more in-depth research before I added it to a tank of my own.
Based on my very small amount of reading, I'd probably be more concerned about it dissolving over time than about toxicity.
There is a link to ask the company questions, that makes these model walls. So I am going to ask them what filament they are using and is it safe for aquariums and non-toxic filaments.