There is nothing to be worried about how the engine is machined with lathe, mill etc. I has two MK-17 Junior engines, the machining is of good quality. Be careful to clean out the engine free for swarf and lapping paste (very rare some engines are not careful cleaned free for lapping paste).

It is a question about the material quality with respect to the hardening method and the material is available where the engine was produced, some time the material was selected who has similar properties as a high quality material, however, is as durable as an engine that was produced by high quality materials.
The model engine in USSR was not allways produced in same factory, some time the engines was produced in school as an education in metal work and sold as a product.

Use the model engine nicely and you will get a great joy of your model engine.