The Klein-Mentor is a German-made camera produced by Goltz & Breutmann of Dresden, the maker known for the Mentor line of plate and roll-film cameras. As a pre-war German product from a Dresden manufacturer, it sits in the collector category of early 20th-century continental European cameras rather than among general-use models.

Documented UK auction activity for the Klein-Mentor is thin: a single tracked hammer result of £480 in 2014 represents the only reference point in our records, so a meaningful range or median cannot be quoted today. Because that figure is a saleroom hammer price (wholesale, before commission), what a Klein-Mentor is worth at retail through a specialist dealer would typically sit higher, and the value of any individual example is highly condition-sensitive.