Damn! I was using this all along!. Removed it immediately and checked the chrome store for an alternative, there's one from Google itself.
https://chrome.google.com/webstore/detail/user-agent-switche...
Is there any way to confirm that this is actually from google though, and not just some 3rd party who chose their publisher name as "google.com"? Most official google extensions have a "by google" badge in the right hand column whereas this one lacks it.
Now, is that trustworthy or not? Good question.
This just has the 'offered by google.com'. I would have assumed a 'By Google' logo would have been added after acquisition?
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.