The biggest question with these sites is whether they are legitimate ways to promote your music, and the general consensus online seems to be that they are not. While they promise real listeners, this is very difficult for the end user to verify, and purchasing plays seems like a way of cheating the system where other artists are building their music up organically.
It’s also possible that using these systems will cause Spotify to ban you, as they are always on the lookout for fraudulent action and fake play counts. This is a difficult area to get into, as it’s obviously hard for Spotify to prove someone is unfairly boosting their followers or plays, and these websites insist they won’t get you banned because they are selling real listeners, not using bots to increase your play count.
However, people have previously been banned in similar scenarios, so you have to consider whether it is worth the risk. There is certainly a sense of something underhand taking place, regardless of what the websites insist they offer, and you can be sure Spotify wants to prevent their users from paying for their plays.