Is a plex subscription worth it?

I want to unlock the ability to view content on my mobile device. I can do that with a one-time purchase (payed with google opinion rewards) or with a subscription. I want to unlock the ability for my entire family though, across multiple devices. Do I have to pay the "one-time payment" for every device? If so, the plex subscription might be worth it. Is there any other major benefit to having a plex subscription?