I have now replaced all but one of the original Canon (5400 series) ink cartridges with the Monoprice equivalents. We have detected no differences in the print quality and have not experienced any printer problems. The cartridges fit properly and so far seem to be lasting as long as the originals. A word of caution: Be careful when opening, as I did get a couple of drops of ink on my hands and desktop. At almost a 40% savings over buying the Canon brand cartridges at Costco, I do believe I made the right choice.
I've been using Monoprice inks for a couple years nowfirst, for a Brother printer (one which ceased to print properly after buying random, decently-rated generic brand off Amazon, after which I switched to Monoprice before replacing the printer), now on a Canon. Buying all 5 cartridgesthe 250 black & all four 251'swould run me north of $70 on Amazon, and a little more in brick & mortar stores. Buying all 5 through Monoprice, even after shipping, and I'm still under $20. Catch them on sale, and it's even more ridiculous. I've replaced each cartridge several times over the past 18 months or so and have yet to notice any issues with print quality.
PROS: - Great price - Great quality - easy to install