Thanks for your feedback! I don't think changing font size is a good idea, but if you feel like I'm wrong, please open an issue with as many details as possible for this at https://gitlab.com/ntninja/user-agent-switcher/issues/new .
I definitely embrace the idea of adding a more clear-cut icon (although I don't agree that the current one is „ugly“) and already updated the icon of my other extension, Smart Refer, because of this. If you could provide a visual sketch of what you have in mind that would help a lot in making this happen through.