I have been working with propellerads for several years now. For all this time I've had only positive experience.
Good volumes of traffic. Possibility of auto-optimization. It is quite stable. I can not say that there are no drops. There are some, but they are minimal. Great customer support. For a long time I have been in contact only with my personal manager and all my questions are resolved as quickly as possible.

The next day I received the compensation because the traffic was of doubtful quality for one of my campaigns, I have sent the screenshots to the manager. Although, I haven't had doubtful traffic for more than a year.

The traffic estimator is very handy. I can estimate traffic volume in advance and set rate for it. There is a great feature of reuse of the same creatives in different campaigns. Quickly up-approaching campaigns.

On the whole, a great source of traffic. Except maybe very high competition in Tier1 countries. But that is everywhere.