Mean you bought 2500 coins and now approx another 2500 you have earned for free? mean without further investment?

Yeah, just let run my masternode and enjoying my daily rewards...
According to my rewards of the last 7 days the average is approx. 40.7 HCs / day. That means you will get another masternode (2500 HCs) in approx. 62 days = double your invest!
Keep in mind that the ROI will change if more mastenodes will be implemented!