Is Format Painter for Gmail safe?

Copies text formatting in Gmail and applies it to other selected text in one click.

This extension adds a format painter for Gmail compose, with access from the compose toolbar, right-click menu, popup buttons, and keyboard shortcuts. It can copy font, size, bold, italic, underline, strikethrough, text color, highlight color, and optionally lists and alignment, with settings to choose which styles are copied. The store description says it runs in the browser on mail.google.com and that email content never leaves the device.