I'm not promoting it actually, and i just bought it yesterday for my HP K550.
Guess why i bought it? - MY HP K550 DOESN'T PRINT black and white documents with 90% full Black cartridge even if only ONE of the colour cartridges are empty. It's a lame marketing strategy employed by not only HP, but also other printer manufacturers.
In this case, I would have to buy an original replacement cartridge which costs RM78 per cartridge.
I was scouting the net for some cheaper alternative cause all the 3 colour cartridges were empty and i'd have to spend RM234 even if i only wanted to print documents in black and white and I came across CISS which is basically a reservoir containing 100ml per ink, kept beside the printer which continuously supplies ink to the printer. Refills need to be only poured into the reservoir and the refills of 100ml per ink costs only RM10.
For my printer the whole set, (plus inks and cartridges) was only RM127!
The price of CISS ranges from 60 - 3xx for different printer models.
So if you're thinking of replacing your old cartridges, give CISS a try! =)
Pics after the jump:
If you see properly, i have made a hole(which looks messy) for the CISS tubes so that i can close the cartridge lid completely. This is only an option and you can just leave the lid open if you'd like.