Avoid them, you'll be greenlit without their help. Most of them are asking for steam keys, so they can make giveaways to promote "their" group. And once your game is released they won't do anything.
Even if their group consist of +10k members, people who join these groups are only looking for giveaways and mostly won't even be a customer once they see your game in a giveaway. Because once a game was available for free, they'll just wait for another batch at some point.
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https://ggtriple.wordpress.com/2015/06/11/influential-steam-curator-group-blackmails-subnautica-developers/Better spend your money on real marketing or food.
(nice trailer! )