For some reason, they put a wrong link on the MP account overview page.
The new Wi-Fi subscription is handled by the same general subscription management interface which also covers subscriptions for United Club, Economy+, etc.
Here is the correct link:
https://www.united.com/ual/en/us/subscription/wifi
Pricing depends on the term and the covered geographical region:
North America and Central America, monthly: $49 or 7,540 miles
North America and Central America, annual: $539 or 82,930 miles
Global, monthly: $69 or 10,620 miles
Global, annual: $759 or 82,930 miles
Yes, I've noticed the discrepancy, same mileage pricing in both annual options, but that's what it says right now.
Subscribers can change the geographic region where they want to use a subscription from the North and Central America region to Global at any time. Subscribers cannot switch from a Global subscription to a North and Central America subscription.
As with the other subscriptions, it is possible to gift a Wi-Fi subscription to someone else.