Dell said don't do it - "we are not providing drivers for Windows 10". My wife did it on her Dell Latitude 13. It works fine although the reboot was rough. Had to hold the power button for a long time to get it to shut down and reboot. Her Latitude 13 has an internal battery which is not easy to get to.
No free upgrade for XP (If you downloaded 10 through the Microsoft Insider Program, you are good to go). Decent surplus machines (dual core, 4GB) cost less than an upgrade from Microsoft so it may be time to kiss the old machine good bye. The download is big so you will want to have a decent Internet connection.
My bank still prefers Windows to Ubuntu ao I keep a Windows machine around just to scan checks. There are workarounds for Linux and an app for my smartphone but my old Canon scanner is still the smoothest platform for scanning documents. Software for Androids is getting very sophisticated and is cheap relative to that for Windows desktops.
So I upgraded the banking machine and it went flawlessly. Microsoft moved a few things around. It seems to work faster and maybe even better than Windows 7. If you are looking for excitement, this isn't it.