I haven't participated in a successful IEO.
But from what I observed, it seems to me that IEO's are attracting investors because obviously it is launched or have the backing up of a reputable exchanges.
The above two statements contradict each other. Dont you think? If they are attracting inevstors they would be successful provided the team is doing its work efficently. So either the investors coming in is a false news or the developers are incompetent. Another extreme possibility is that the project was just a cash grab from the start.
So for projects, no need to market it or at least spend a lot of money.
Marketing is an essential part of the project if they want it to be successful. Its not necessary but it helps.
As compare to ICO wherein there are so much hype around it and will open up bounties here in the community. But the sad part is that most of them failed and are not paying their hunters.
Which was why ICOs came back in a new "disguise", rebranded themselves as IEO. Same old bullshit, just a new persona. Typical methods of scam.