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I don't really see a problem. The accounts are public anyway. And if you don't want that afterwards, you can simply end the friendship.

Exactly, I can't come up with any potential downside, only benefits. It would lead to simply checking the progression in-game rather than opening all contenders' PoE character page every 30-60 minutes. ^^

Upsides also include strengthening the community. You don't have to play with each other for there to be interest in how others are doing, what they're playing, what they're enjoying, and just conversations while playing.

I'd start with it being a suggestion, rather than requirement (and not sure how you'd enforce the requirement anyway...)

Cheers. If it weren't a condition of entry then anyone opting out would have an unfair advantage, though? In that other competitors would need to navigate out of the game to check on his/her progress?
I very much doubt it'd be a problem with our current entrants. You're all here for the love of the game.
(Less than $10 prize money for 24 hours of intense focus is hardly going to bring out the worst in people)
That said, if Steem hits $20, and each of the class prizes is worth $400; I'd rather not have people disadvantaged by their good sportsmanship.
If there's no technical reason that a player would be unable to send and receive friend requests and it makes the process easier for everyone, then I'd rather make it mandatory from the get go.
We still have a few months, though. I'm very much open to suggestions.