The FinTech company I work at offers ESPP and an option to invest in company stock for your 401k. I take full advantage of ESPP but sell it quickly. My coworkers have saved it and been through 3 splits and made a ton of money. The same coworker lost 10s of thousands when he worked for WorldCom/MCI in the late 90s. He’s probably even right now.

I would never invest 100% of my 401k into my employers stock. Even 10% seems risky.