[jayass]

Well, yes and no. By enabling the developer mode you can install any extension that was not verified by the google web store policy.

As long you are careful with the extension you install manually you should be fine.

[ThunderSizzle]

Is there necessarily any more danger than installing a random exe from the internet on a typical Windows admin account with UAC turned off?

e.g. from https://windirstat.net/download.html