The most striking difference from the ICO and IEO is that the IEO cooperates with Exchange to sell their coins while the ICO does not directly cooperate with Exchange. But ICO and IEO also have their own advantages and disadvantages.
IEO have it's advantage since it is already listed in exchanges, but the risk is always there when we don't invested in time to research it and if we must learn to research may it be in ICO or in IEO cause it still depend on the project if it will succeed.