This source confirms the exact opposite. The extension install can be prevented by using the documented group policy.

Additionally, it looks like this is a product intended for enterprise deployments, where the admins would probably already be comfortable with managing group policies. This is basically how software ends up on your computer in big companies.

Because otherwise you could be like Deloitte and have some jaggoff management consultant leak all your clients' private email addresses because they didn't follow internal technology policy and used Google Docs to stow it all.