The engineering on these is well established to the point to where the patents have expired, and Chinese factories are able to build to the original German specifications for pennies on the dollar. This is why you’re able to get such a good deal with something like Vevor or Hcalory. At this point, I don’t see any value in getting a system that is more expensive than $200 or $300. Unless of course, you wanna get one of those fancy gasoline heaters instead of a diesel heater. With that said, this design was originally set up to work with diesel, and the gasoline variants tend to be less reliable, especially at elevation.
I have rabbit holed on this pretty far, built out a van that uses one, and run maintenance on it as need be. I depend on it for warmth in my van at least 20 to 40 nights a year both skiing and hunting. I wouldn’t get anything more expensive than an Hcalory as I’m not convinced that I would get any extra value from anything more expensive.