How reliable or trustworthy are LTSPICE demo circuits?
According to my experiences, all simulator are just simulator, they rely on how precise your models are, and how precise your circuits are, such as if you take all the parasitic factors into consideration. This is particularly true for power supply designs.

In my opinion, LT's demo design (not just LTSpice demo circuit, i mean demos with demo board) usually have high quality. So i recommend you to reference their demo boards design. I think them are more reliable than the LTSpice demo circuit.

In your posted .asc file, you'd better go to the similar demo board: DC1961A - LT8309ES5/LT3748EMS Isolated Demo Board | 36V ≤ VIN ≤ 72V; VOUT = 12V @ 5A.



Update:

I don't mean simulator has no use, they are very useful indeed, they can help you to verify your ideas before throwing so much money. But if you want to find a reliable reference demo, demo board may be more reliable.