Jim Cramer weighs in on Slack (WORK) going public Thursday.

The reference price--not its pricing point, since it's not IPOing--for Slack's direct public offering Thursday was set at $26 by the NYSE.

However, Cramer's got some advice for investors who are wondering if it's worth buying Slack.

"You can own a Crowdstrike (CRWD) or you can own a Zoom (ZM) or you can own a Slack but don't own all three," Cramer said.

"Do not own all three because these are what I used to call in my book Real Money. The red hots and the red hots are remarkable, they popped up in 1999 and they're back," he continued. 

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