I think telegram is also good and many people discuss about ico project there, let alone usually information from ico is always updated.
Im using Slack for interesting project for me. Its more better for me. I cant see problem in slack bot.
It's not just the slack bot. There are already other "user joining" who is sending private messages to people telling them they are from the team (name of this user are mostly similar to team members name) and there would for example be an special pre-sale or that the sale itself is open with extra conditions or in channels where the sale is over, their would be an extra round. I am in some slack channels and two days ago I nearly got every 5 minutes a message.
"Dont easily trust something before you check it out"