I heard that Pinterest has to issue NQOs instead of ISOs to do this. If that's the case, they come with their own potential downsides.
Having ISOs matters most when the underlying shares are illiquid, and you can defer the tax obligation until a sale event (provided you don't hit AMT). When you have a 7-10 year exercise window, the company will likely have IPO'ed or have failed. The tax benefit of ISOs are greatly diminished.
I think people downplay how easy it is to hit AMT. A single, no dependents, standard deduction filer making $120k will hit AMT after $26k of on paper gain for ISO exercise. Everything after that will be taxable. Filing jointly, 2 people who each earn $120k can absorb $18k in on paper gains from exercising ISOs. Add in a kid and it drops to $15k.
That's a paltry sum, basically breaking any advantage ISOs provide.
It's a rough situation and something needs to change.