OCP inks in a Canon ix6520/ix6550, for the record...
I did also use InkJetFly inks in my (now defunct) R1800.
For an amateur who doesn't sell prints, cutting the price of ink by 10 is not unsignificant. Especially when there are few compromises involved (for OCP inks : none in print quality, but maybe some in print impermanence, it's a dye printer anyway).