Is it really more difficult to keep track of than regular shares? It's easy to decide if the stock might be purchased: if the IPO/acquisition is priced above strike price, then they obviously will be bought, and otherwise will not.

It is indeed not useful to the company, and a great upside for the employee. Out of all suggestions in the article, this is probably the most employee-friendly. But that's not a bad thing if it helps recruit good employees, or otherwise seems like a fair thing to do.

The usual 90-day limit makes employee vesting almost meaningless. They either wait for an acquisition (and get all their options accelerated), or leave before that (and lose all of them). Few employees have enough spare cash to buy out their shares.