Most of the altcoins I've bought have under performed when compared to Eth/BTC. I'm a long-term believer in COSS, however. With COSS you get paid out dividends collected from the site's transaction fees. I'm really hoping their site takes off and starts paying out a lot more. If the exchange grows as much as other exchanges, it can be a very profitable crypto to invest in.
COSS started as very promising alternative to regular exchanges by using the concept of reward based on the amount of COSS token held on exchange. Due to fascinating concept, it first raised $5-6M, then gathered users on large scale and then value of token rose 4-5x. But after the intro of DEX like IDEX, use of platforms like COSS diminished. Main reason for that is the withdrawal fees charged by COSS to compensate COSS holders is very high. So I don't think it is wise choice to go for COSS now.