Yeah I used to join private PreICO but you must do your own research about the project, team members, social media, slack, icorating or reviews and read the whitepaper carefully and TOS of ICO. I have no problem with PreICO so far but you must be confident about the ICO since ICO are not risk free investment. Personally I only invest in PreICO with short roadmap and token distribution because I dont want to lock my money for long time.
Many projects are quite interesting and when you invest in them you can get a good profit. But investments on the PreICO stage are too dangerous in my opinion, although they offer good bonuses.