Good point Ed. I'd also like to add that lens coatings are just as proprietary and varying as any of the other components of scopes and binoculars. It's very hard to compare coatings from different manufacturers because the type, quality, and formulas used in the manufacturing process are so different, even if the end goal is the same.

The most simplistic rule of thumb that can be applied is to always look for "fully multi-coated," which means every lens surface between the objective lens and the eyepiece lens has the same lens coatings to facilitate reflectivity and light transmission. "Multi-coated" means that only the exterior surfaces are coated, usually for durability over light transmission. That doesn't mean that a multi-coated optic is necessarily worse, it just means that fully multi-coated optics will usually have better light transmission on paper.

To be clear, most branded manufacturers utilize fully multi-coated optics and prisms in their quality offerings. It's the dollar store stuff that you have to pay attention to. If it's not explicity labeled, chances are that it's not.

Also, there's a bunch of variables that come together to produce the quality of the image you see when looking through a bunch of lenses. Aperture size, magnification, number of lenses, clarity, sharpness, lens coatings, chromatic aberration, field of view, focal length, field curvature... it's all a very complicated, so Ed's warning is very accurate.