AFAIK, there are no published reviews specifically of the GB mics. There may be reviews of branded versions of these mics, but of course we don't talk about those here. It also isn't necessarily the case that similar looking mics have the same electronics/ribbons, etc. Some of the GB mics are (or were) completely unique to the GB. The ACM-310 for example. There are a couple threads here where previous GB mics are reviewed by purchasers.