its depend on project quality.but listing guarantee will be another thing for investors while decide their investment.IEO give certainity investors to trader their token/coin, meanwhile ICO could not do that.
sometimes there are also ICOs that have been registered in exchange but they have not opened a trade. it is also good for our study of the ICO project like that. actually IEO or ICO is the same, because I see projects not from ICO or IEO, there are more important factors for us to see.