In general, IEOs might be a little bit safer than ICOs.

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Especially IEOs come from well-known, reliable exchanges, like those one you listed in the OP.
In contrast, for IEOs come from un-known, young, new-born, small volume exchanges, they are more risky and it is difficult to judge that invest into such IEOs is safer than invest into ICOs.
Exchanges can make scam exits, can get hacked and go into dead/ bankcrupted, so it is obviously risky too.

Additionally, it is hard to say IEO invesment is safer, because even exchanges don't got hack, or scam exit, investors can get losses too.
Buying at highs, selling at lows, and eventually get losses as ICO's invesments.