I bought around 0.01 BTC with that OCEAN IEO by Bittrex, and just because I missed it, it was dumped to a very low price. It became 0.003 BTC. It's not a great thing to experience and I think I would't invest with that unless I would be able to catch the time everyone would sell. I think that's just how it is going to work and will work.
Bittrex is one of the oldest and most trusted exchanges in the crypto space. They are a good exchange with a track record of success across the globe, of course, their IEOs are to be trusted. I haven't seen anyone complain about ill practices or getting scammed by participating in IEOs on bittrex. I strongly think they can be trusted.
It's not the exchange that should be the blame, but the people investing in it and selling the moment it goes live with trading. That's just the reality.