i think, an ieo of a big exchange is very safe and offers more protection than an ico. a sto is also quite safe, but only if you can find an official confirmation of an authority for it.
without such a confirmation anyone can claim that he organizes a sto. in this regard a sto is as uncertain as an ico.
Hat is the issue, I have seen some project claiming to be STO while they are not and the only STO project that I think we have now and confirmed is that of bit bond, I don’t know how completely genuine the rest I have been seeing are, but that is not even my priority when it comes to choice of mean of investing.
I think my major priority now should be IEO, he fact that IEO has not direct influence of government and yet still regulated successfully internally should really be applauded, and I think for now, when it comes to IEO with Binance, it is still very safe and coupled with the fact that you get you investment increase as quick as possible.