IEO are just ICO with partnership with exchanges. They are no different than any other ICOs but the exchanges that they are hosted on promises to have thoroughly investigated about the project and are green signaled as useful. So, there IEOs have better exposure with potential buyers.
It will be a new way for the project to gain the investor since the ICO will not work too good. They make a deal with the exchange, and I see that the previous project can reach their cap in the early stage. But I wonder, what will happen after the IEO is finished, did the tokens or coins will get a list on that exchange or they need to wait for a while so the investor can sell the token or coin to make a profit.