Using a hardware wallet is a good idea. What do you mean by "use it with 3"?

The myetherwallet phishing scam is not only on Slack. Using Slack is not an inherent threat to myetherwallet. All you have to do is avoid clicking on links from unknown sources. And always verify your browsers address bar is correct. In the current phishing scam the domain has .im added to the myetherwallet address.