I think they are comparable to the Big Three. It depends on what your expectations and experience level is in that regard. If you have a trained eye you might notice slightly more color fringing especially in the outer 1/3rd of the image. You might also notice a slightly warm (yellow) color cast to the image. Beyond that, in terms of image quality, there really is no difference to my eyes. They offer a very bright, sharp image from almost one edge of the field of view to the other.

In terms of build quality they are top notch. I would put them right up there with the Leica Trinovids in terms of overall durability. However, they are not quite as refined in some ways as the Big Three.For one example their eyecups are entirely functional but do not offer the multiple clickstop adjustments that the more expensive models exhibit.

Still at less than half the cost of some of the Big Three's comparable configurations they are a steal in my opinion.