Using these sites are basically pointless. Anyone who gets their subscribers this way can be spotted a million miles away by any real YouTuber. Story Time: There was once a guy who wanted to do a collab with me; he had tens of thousands of subscribers, but upon inspection it was obvious he got them by sending out thousands upon thousands of contact requests, so none of his subscribers were organic. Needless to say, his videos had a disproportionately low amount of views compared to his sub count (a few hundred at best), and his videos were basically crap.
Did he violate YouTube TOS? Probably, but either way he didn't get anything from it.