Take a look at my post and you'll see that I liked the printer and I loved the Instant Ink service, so much so that when my free trial was over I started to pay for the service and I still am a year later. I think that speaks for itself and I can honestly tell you that in the two years I've been using HP Instant Ink I have never run out of either a black or colour ink cartridge.
I'm not alone though as the HP staff told us that once someone has signed up to the programme there is a 98% retention rate. You don't find that level of satisfaction much nowadays. So how do HP know when I need ink? Well my HP printer is wifi enabled and as long as I turn it on regularly it sends the info all on its own and my ink just turns up by post before I ever even realise I might be getting low. It is very good.