I have just had my second try at refilling Hewlett Packard inkjet cartridges. This is something I have tried before with varying degrees of success and more often failure or at the very least success with messy fingers.
Refilling cartridges does appear to make financial sense, I have an HP Photosmart D5460 which produces awesome colour photo output, at present a set of cartridges is around £80 and that is more than 50% of the purchase cost whilst a complete set of inks with the refill tools (the modern ones are good) cost around £23 and I think will do around 4 refills (the box says 5 but with it's hardly an exact science).
Clearly there are downsides to refills (besides messy fingers), chief of which is uncertain print quality and uncertain robustness of the inks - if you are printing photos to display / keep for a long time then sticking to HP manufactured cartridges is essential.
But what if you just want the odd snap to show people and are not concern about longevity? Or you are printing web pages / text for convenience of your work / hobbies (so we print web pages to have a hard copy to refer to when working off screen quite frequently)? Who cares how long the colours stay bright.
I have purchased a set of inks from Inktec. I don't recall any magic claims about longevity of the colours but they are supposed to be consistent colour blah blah and they come from a business specialising in refills - there are plenty of cheaper sources out there, particularly ebay. These come with tools which actually work, the instructions are good but take a couple of goes to figure out.
My experience? Well I have found my HP D5460 cartridges have a little ink window on the bottom that fills with ink, once I realised I monitored how full that was (hold the cartridges the right way up as the ink simply sinks down into the window) and that is the indicator.
The big trick with this HP5460 is the software. HP have been very clever to make sure you keep buying their cartridges, the printer bleats if non originals are used - firstly, refilling the existing cartridge is a disaster as the printer keeps saying the the cartridge needs replacing. So the trick is to have 2 sets of cartridges so refilling the "old" set means the printer just tells you that you've inserted a previously used cartridge and asks you to press ok. Job done.
These refills are great. Just remember to refill over a sink.