IDEX is one of the legit exchanges and I used it twice for selling my tokens. I would say it's like EtherDelta and Forkdelta the interface is quit intimidating for first timers.
I do agree that if you are first timer on using up these decentralized erc20 exchanges you would really be confused on their interface but somehow they do really have guidelines which would really be suggested anytime to read up before using up the exchange.
Yes IDEX exchange is legit. idex support a lot of 20token REC. you can buy sell token on idex. Sometimes idex is also often unpredictable.
What unpredictable? Its always been unpredictable when it comes to prices just like on other typical popular exchangers too the difference on here is that this is a decentralized ones but rest assured this is legit.