I think there are no cons and this is a great idea.
First, a 6+ year vesting schedule protects you from the less committed founders. The last thing you want is the flakiest founders quitting early and ending up with as much stock as you, or close to it. The fairest, simplest, most win-win way to protect against this is a long vesting period that more accurately maps to the 7–10 years it takes to IPO / Go Big.
More on that here: A Simple Commitment Test For You And Your Co-Founders
Second, a Double Trigger (you get 100% acceleration if you are fired after an acquisition) has modest upside but no downside and makes people feel good. There’s an argument that especially VCs make (and one with some truth) that a Single Trigger can harm M&A outcomes and create issues in acquisitions. That may or may not always be true, but Single Triggers definitely create some issues whenever they exist, and almost always create frictionful re-negotiations these days. You just don’t see CEOs walking away 1 day after an acquisition anymore. See, e.g., Jet. So a Single Trigger certainly can be bad for many parties, or at least, can have negative effects.
But I’ve never seen a Double Trigger impact an acquisition negatively. “Worst” case the acquirer renegotiates it, and/or cancels it (yes, this can be done in M&A documents), and you lose it. Well, you are at least no worse off in that case.
Still, a double trigger is a great security blanket. It makes founders (and VPs of Sales) feel much better. Like they aren’t going to get scr**ed. So just do it for the founders and your VPS at least.
Really I see no cons and as an investor and founder would support both strongly.