With these cheaper Chinese units the brightness mismatch btw left & right is normal. Here is a telling comarison between the cheap and top Baader units:
http://www.pbase.com/mclemens1969/image/68856060
Based on what I've read only, and quantitative analysis of images in this review:
http://www.astromart.com/articles/ar...article_id=169
the best left-right matched of the budget priced binoviewers would seem to be the Denkmeier Standard. (In fact it seems to have better balance than the Denk II.)