It goes like this..... you sign up and select the required printing papers each month and set up a Direct debit each month and ink is sent out accordingly
£1.99- for 50 pages each month
£3.49- for 100 pages each month
£7.99- for 300 pages each month
There is a rollover so if you use less pages each month they are rolled over to the next month and if the next month you'll need 300 pages you just log in and update so you can change your tariff each month.
This is way cheaper then buying cartridges and gives you piece of mind because when you are about to run out, Ink is sent out in the post. Excellent solution from HP. Follow the link for more information.
And if you buy a HP Printer they come with free 5 months. I brought the HP Envy for £35.00 and this promotion came with it. The price of the printer is now gone up.
Well worth it :)