Due to lots of scams and frauds then its never been recommendable for you to join up those paid groups.Unless if they were free then you could really join up if you wanted to.
Even for free, most of those groups has something for you to take even they don't charge you. And that's your participation to the ads that they might send to their members.
If you think that you're okay with that and that's the benefit that they can only get you in return of earning some good rewards from their signals, it's up to you if you're totally okay with that exchange.