Win 10 has turned out nowhere near as bad as I had been lead to believe by all the comments I've seen in various places.
Knowing that in due course SWMBO would insist I updated her laptop I decided to upgrade mine (dual boot Win 8.1 Pro and Mint Cinnamon) over Xmas and see how it all went.
I made images using Clonezilla at each key point in the process (including the fully patched and up-to-date Win 8.1 and Mint installs, before even starting), expecting from what I'd read to have to at the very least go to some trouble to get the dual boot working again - and that's assuming Win 10 hadn't gratuitously destroyed Mint while installing itself.
Win 10 was eventually installed and behold! - the dual boot was totally unaffected. Next step, install various means of killing Cortana, Bing and telemetry - and make another disk image.
After some updates, including "important' security updates, check everything; no, none of the settings I had made have been changed and CBS (Cortana, Bing and Slurp) are still all firmly disabled. The next step - activate Bitlocker. Part way through this I realized it was going to take forever to finish because I'd set encryption for the full Windows partition, so I powered down the machine and restored from the previous disk image - once again, all fine and as I'd left it, including the dual boot.
Second attempt at Bitlocker - sectors in use only this time. Much quicker, but after a couple of days I decided I didn't want encryption at the moment, so once again load the Win 10 + Mint image - still no problems.
So far the only complaint I've got with Win 10 is that it doesn't tell me when it's updating - but I can easily kill the auto updates anyway by disabling an extension in Chrome that allows it to intercept search requests headed for Bing - for with Bing blocked and nothing else intercepting and acting on search requests directed at it, Win 10 doesn't seem to be able to determine if there are any updates available - in fact, it reports that it is unable to contact the update server.
At this stage Win 10 will be staying on my laptop, along side Mint - although just in case I've got images going back to Win 7, which is what the machine originally came with - a large beer for the person who invented the high capacity USB 3 portable hard drive.
Now, if only I could get Mint to work with Sky TV!