Pro Tip: If a large financial institution tells you they are protecting you, they are bald faced lying to you and you are about to get a serious lesson in business.
The same idiots who tell you that IEX is a good thing will also sell you actively managed mutual funds that A) under perform vanguard and B) seriously under perform once you subtract fees.
Rough recollection of a couple of paragraphs in the book. Someone else please add if recalled incorrectly.
There are a lot of SEC comment letters claiming IEX's delay coil is an "intentional device"[1][2] but the SEC approved their exchange application because they consider the delay to be "de minimis." One area where the IEX delay differs from simple geographic latency is that IEX delays incoming orders, outgoing fills, and outgoing market data, but they do not delay market data from other exchanges. That difference makes it more difficult to "pick off" a stale order on IEX, but on the flip-side, it also means IEX orders get to free ride the price discovery happening on other markets without taking risk.
This delay also raises issues because under Reg NMS, brokers have to route orders to exchanges with the best price when trading through an entire price. Since IEX's data is lagged, it may be showing a quote that is no longer accessible. Brokers would face additional slippage/execution uncertainty if they need to route at this phantom quote and wait 700 microseconds to find out it wasn't there. Canada has exchanges with delays similar to IEX, but IIROC ruled that they are not "protected" quotes so brokers have discretion not to route there if they feel it would harm their execution quality.
Or find a way to route around the 30m cable...