This is the standard high-capacity black ink cartridge for Canon Pixma MX860 and MX870. I owned the first printer up to a month ago, and then I replaced it with an MX870. Note that the printer has additional 4 photo color ink cartridges (221-BK, 221-C, 221-M, 221-Y) for a total of 5 cartridges.
The only negative is the price. I suppose there are no truly cheap genuine ink cartridges anywhere.