In an era where security is the top most criteria for choosing a good exchange particularly when considering the rate at which big exchanges are being hacked, it is good to check the security record of an exchange before using it.
Coinone has been in existence since 2014, and till date it has not been hacked. It has recently improved it's security by partnering Certik and xangle.
It is also believed that another reason the exchange has been insurmountable for hackers is because the CEO, Cha myung Him was a former likely an ethical hacker hence it is possible to cover all loophole.
The exchange support many cryptocurrencies particularly the major ones like BTC, eth, ripple and litecoin. It also support tokens numbering into 40s.
It charges only flat fee of 0.10 from makers and takers although the withdrawal charges of 0.15btc is somehow too high.