That's a great question. I essentially gave everyone access that requested it.
It did give me a chance to set expectations that it was very early stage, this created a very forgiving and engaged early user base who helped me figure out the product. Some of them have gone on to become our biggest advocates.
I was also able to get on the phone with just about every one of them. This was invaluable for honing the pitch and the product. Also, with so few users early on, I was able to make changes to the SDK on demand and refine the API.
The obvious downside was that it may have scared off people. I'd like to go back in time and redo so I could see what works out better. I think just opening it up could have a bunch of benefits too.