It's interesting, if you go to the support tab and follow the link to the maker's support website, you end up on https://spoofer-extension.appspot.com/ The contact page there links to "Glenn Willson" as the author - and their G+ page has a link to The User-Agent Switcher Has A New Owner: Google! http://www.glennwilson.info/2017/02/the-user-agent-switcher-...

Now, is that trustworthy or not? Good question.

Search for an official Google Chrome extension (such as Chrome Remote Desktop). You'll see a 'By Google' logo (https://chrome.google.com/webstore/category/collection/by_go...) as well as an 'offered by google.com'.

This just has the 'offered by google.com'. I would have assumed a 'By Google' logo would have been added after acquisition?

If you go to the listing of all Google extensions (the URL you linked) and open the "Chrome Sign Builder" Extension, go to Related -> "More from this Developer" you will find the User-Agent Switcher for Chrome. So it does seem legit.

Well, the LinkedIn checks out too: https://www.linkedin.com/in/wilsong

Of course, forgeable as well.

I've sent an email to his anonymized domain registrant contact to see if he can do anything about his malicious competitor.