Much appreciate the various inputs on this - so here's my final thoughts on the issue.
For many years we used HP all-on devices on each desk, running 5 at one point (8600/9600products) and these proved to be solid, reliable machines giving many years of service. We kept costs under control using Monkey Office Equipment compatible cartridges ((from their Q-Connect range) with little or no problem.
The ongoing battle to 'hide' the machines from HP (so they didn't lock-out non-HP cartridges - and in addition I have a deep suspicion of their data mining and its potential risks as a hacking route) became more and more difficult and as the machines started to exceed 5 years + of heavy use, we started to switch to Xerox laser machines.
We rather liked the Xerox machines (used nothing but OEM consumables) and although our costs went up 'per page', reduced volumes made this acceptable. However, we had two machines fail (both locked out immediately after drum swap) over the last 12 months. Xerox 'customer services' were appalling, although one of the machines is to be replaced under warranty in 5 - 10 working days (promised 11 working days ago after over a week of phonecalls).
I grabbed the HP 9010 printer (the modern equivalent of the models we used to use) as it was cheap and available quickly (delivered and running 1100 next day.
It offered (on the face of it) 6 months HP Instant Ink which seemed to offer an acceptable saving - in fact, on investigation the 'Instant Ink' deal isn't badly priced anyway for a medium range user.
However, to use the 'Instant ink' service at all you have to allow some level of external internet access and control (which concerns me deeply - and offends my interpretation of fairness), as well as the fact that they 'turn off' your cartridges if you ever cease the contract.
What I hand't realised (and annoyed me further on discovering it) is that the 6 month free trial was dependent upon signing up for 'HP+' (a series of what the described as benefits, including remote printing and diagnostic, none of which I want). As I consider this arrangement further increases potential security risks we have declined it again and will pay for the HP Instant Ink service from day 1.
On a further point, the build standards of the new machine appear nowhere close to the previous models - so i can't see this being a 5 year + machine.
We await the Xerox replacement and will probably then replace the other Xerox machine (about to start researching that), as Xerox have no interest in even talking to us about problems with an out of 1yr warranty machine, and give the HP device away at that point.
One thing is certain, we will not be returning to the HP fold.