As you know, current users of Windows 7 and 7 acan upgrade free to Windows 10. If you change you mind, you can go back.
Yes, it is true. You can revert to the prior versions of Windows and not lose your data. Microsoft has made it easy for those of us who are reluctant to move ahead. Built0into the new Windows 10 are tools to let you go back. So what is the catch? Nothing.
You should not destroy the extra files Windows makes to save you old settings and system. These are needed if and when you want to roll back the system. And do not use the disk clean up or any other tools the sweep out extra files.
Even so, it is always a goo idea to have a reliable backup plan in place. Just in case. If need be, you can install Windows 7 again and get r data back fro the backup. Hopefully that should not be needed.
Still in doubt? Here is a tip. Get another Hard Drive and try Windows 10 on the spare hard drive and see how it works before you commit yourself.