From the ChangeLog:

• New single-window UI.
• Performance MX leds show the current battery charge.
• Support the VX Nano mouse.
• Faster and more accurate detection of devices.
• If upower is accessible through DBus, handle suspend/resume.
• Replaced Solaar icons with SVGs.
• Running solaar-cli in parallel with solaar is now less likely to cause issues.
• Bugfixes to saving and applying device settings.
• Properly handle ^C when running in console.