Google One VPN is the new service added by Google in their Google One plans. This is available only for a certain plan and above. As of now, the VPN service is launched in seven more countries right now.
As of now, you can only get the Google One VPN if you subscribe to at least a 2TB storage plan. And even if you purchased the 2TB storage, you need to be a resident of Canada, France, Greece, Italy, Mexico, Spain, and the United Kingdom. For the pricing, you have to shell out $9.99 a month, or $99/year.
However, if you are on the cheapest plans, including free 15GB, and below 2TB plans cannot get the VPN services separately. Although, you can use the VPN for various security reasons such as protecting sensitive data, etc. the major disadvantage is that you cannot change server location at all.
Another issue or none, whatever you consider, is that you can use the services right now only on the Android platform, with Google working on the iOS client and might launch in the coming days.
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