I worked for AECOM 20+ years ago and we could buy shares and got some multiple free, like pay $10 abs get $15 in shares. They had an accounting firm calculate a share price each year.
They ultimately went public and I was able to liquidate on the open market. It was a good investment for me.
I don't remember what it would have taken to sell but I seem to recall it was fairly illiquid. I think I could have sold them after the vesting period if I was still employed, but I was not.
I think of it as giving the firm a loan to grow. If the firm doesn't grow profitabley, your shares will not go up.