Machine with top features but supplied toner has apparently only half reach

The unit like it very much, great prints and super functions (scan to network, emails and so on). But what displeases - see attached picture: An original cartridge has black 131A lt a range HP 1600 sheets.. The supplied cartridge is already empty after about 900 pages (normal text printouts with increased proportion of black). Because of the favorable purchase price into perspective again.