This is the same as investing into ICOs isn't it? You want to check their team profiles, whitepaper and the community? With IEOs there's just an extra factor of having an exchange there.
Keep in mind, those are the well renowned exchanges but the projects might not always be good - all of those exchanges will pump the projects tokens during the start of the free market and projects don't end up getting all of the funds they raised.
I think that choosing IEO in a very popular market will shorten our research. all we need to do is look at the project team, the concept, and also the partnership. I understand when a market does not want to lose its reputation just because of 1 IEO from an unclear project. so, seeing the market can make many things imaginable for a project.