In regards to COSS, I have read all their interviews with the core team members + keep up to date on their twitter and reddit. I have read their whitepaper and done all the research I think is necessary including looking at competitors.
I think they have a promising idea with a team that is gradually getting more and more qualified. They still have a long way to go but I feel they are the most professional and least shady exchange I've used (including Bittrex and Binance, not including Kucoin because everyone knows it's shady).