The only problem I've had with Windows 10 so far is with High-DPI screens. Positioning of screen elements on such screens (usually tablets and laptops) will be out of scale, too large or too small. Granted, this is not specifically a problem with Windows 10, you probably would experience the same problems in Windows 8.
If you're on Windows 7 and don't have a High-DPI display, you'll likely be fine upgrading in-place. If you have display issues, give the following download a try. You can always run it in demo mode to see if it helps before you commit to buy/upgrade.
www.celestialsoftware.net/telnet/AbsoluteTelnet10.14.exe
Let me know how you make out!
Brian Pence