As I've said elsewhere:

(a) There are other existential risks, not just AGI. I think it more likely than not that one of these other existential risks will hit before an unfriendly AI is created. I have not seen anybody present a coherent argument that AGI is likely to be developed before any other existential risk hits us,

(b) Even if AGI deserves top priority, there's still the important question of how to go about working toward a FAI. As far as I can tell, working to build an AGI right now now makes sense only if AGI is actually near (a few decades away).

(c) Even if AGI is near, there are still serious issues of accountability and transparency connected with SIAI. How do we know that they're making a careful effort to use donations in an optimal way? As things stand, I believe that it would be better to start a organization which exhibits high transparency and accountability, fund that, and let SIAI fold. I might change my mind on this point if SIAI decided to strive toward transparency and accountability.