I found the following information in the New Goods section of the 1935 British Journal Photographic Almanac:
THE “OPTOCHROM AUTOMAT” ROLL-FILM DEVELOPING TANK (Sold by Sands Hunter & Co., Ltd., 37, Bedford Street, London, W.C. 2.). The Optochrom developing tank is designed for daylight loading and development of roll-film, and has a neat and ingenious construction. The film is loaded into the tank very much in the same way as into a camera, and then the backing paper is carefully pulled out through a slit specially provided for this purpose. The ease of this operation is shown in the illustration. As the paper is pulled out, the film coils itself round a series of spirals inside the tank, so that when the paper finally comes away, and the slit is shut for development, it is naked and evenly spaced inside. Development follows in the usual way, and a filling funnel is provided at the top of the tank with a generous lip to avoid splashing. After development, the drain plug at the bottom of the tank is removed, and the developer run off and fixing solution substituted. For washing, an attachment is provided for a rubber tube to the tap, which screws into the filling funnel. In this way the tank may be left to wash with the tap gently running. The tank is well made in moulded plastic material, and the various parts are easily separated for washing and cleaning. At the price of 35s. for 2¼ x 3¼ films (special thermometer 2s. 6d. extra), the Optochrom tank is a very interesting proposition, and should be of great interest to all roll-film amateurs.
The condescending tone in the last sentence was typical of photographic publications right up until the 1970s. Mere amateurs used film; professionals used plates. Remember then that 120 film was officially classed by some silly organisation that considered such trivial matters as a ‘miniature’ format. Only much later was the word restricted to 35 mm cameras.
In present money, 35 shillings was £1.75.