Yeah but they don't give 2 signing bonuses right? That seems downright weird from a terminology perspective... how can you legally have 2 signing bonuses if you sign only once? :)
They mean that the signing bonus is divided into two yearly payouts instead of one. It's a single bonus.
I personally don't see what's wrong with a N/2N/3N... vesting schedule for post-IPO companies. You're buying in long term, that's the deal. Is it sided to favor employee retention for the employer? Sure. The overall comp at AMZN is pretty competitive though. That's the deal.
It makes more sense for a fiscally stable company like Amazon, which actually sees reliable stock growth and a real business model as compared to snap with neither of those things-- but that's not a criticism of the vesting schedule, it's a criticism of snap's true value. That's the thing that would keep me from a company like that, not the length of my RSU vesting periods.