I believe in Flash Boys the issue is not HFT itself but that the way the market provides access favors certain parties. I could be wrong though, I've only seen the (somewhat related)documentary on the subject some time ago.

IEX is not an exchange. It is a dark pool with technology, rules and special order types specifically in place to give large hedge funds advantages over "average" investors.

They still allow collocation, venue arbitrage, and non-human timescale trading. Any electronic trade you could do on any other dark pool you can do on IEX.

The main difference between IEX and other dark pools is that they are owned by hedge funds and they either duped or bribed a famous author to write about them.

[edit] The comment below correctly points out my insinuation about bribery and Michael Lewis is unfair and snarky. I will point out that Michael Lewis wrote a glowing book about Jim Clark a decade ago, who happens to be an investor in IEX, so there is at least the potential for intentional bias.

"they either duped or bribed a famous author to write about them" is that just your personal opinion or do you have any evidence to back this up?

Let me save us all a giant subthread:

https://news.ycombinator.com/item?id=7531429

All of that is just marketing talk.

IEX is currently not an exchange. What they offer is a dark pool connected in series with a Smart Order Router. That's what all the big brokers (e.g., JPMorgan, Morgan Stanley, Goldman, Deutsche Bank, etc.) have been offering to their customers for years and their dark pools usually offer a lot more liquidity. The big brokers have become better and better and smart order router technology to protect their customers as much as possible from HFTs. IEX is at least 5 years late to the party.

Perhaps they are planning on becoming an exchange one day, but I am not sure how they can do that while slowing down order executions. It seems to me that that would be a serious violation of Regulation NMS.