My thought is for support reasons alone, you should have upversioned when it was a free offer. There is a load of nosey parker defaults and restrictions you might wish to change when you eventually make a move. Whether it is worth the cost now the offer no longer applies, if you are happy on W7, is debatable. How flush are you at present ?
Very stable - a lot of the people I help havent needed to contact me so they must be happy. Provided, as other contributors say, you turn off all the communication bar location and fault reporting and backup ALL your personal stuff prior to updating its very good. I`d recommend a full installation rather than an upgrade as it clears out all the old stuff but takes a while longer.
At the top of the start menu is 3 parallel horizontal lines, click on that and then settings then privacy and pick your way through that list turning off things you dont like the sound of.
The main worries of changing over for me are that I've got specialised hardware (a professional level film scanner and a decent graphics tablet) for which there are no W10 drivers available. I also use older versions of expensive software (such as Photoshop 6.0 and QuarkXPress 4) which will run on W7 but which are unlikely to run under W10. To update QuarkXPress to an equivalent product would cost me £709. To get the full features of Photoshop would now cost me over £240 per year. Putting together those costs with similar costs for 'professional' software and for replacing my specialised hardware would cost me in the region of two thousand pounds, so I'm not rushing to do it!