I suspect it's more because some rando could actually try to use it in public space. The invite only means they could send it to people who will give them good PR, are known not to be idiots, and can be invited to sign many responsibility disclaimers.

That makes a ton of sense, yes! To be honest, I was wondering less about their reasons for invite-only and more about whether this kind of gentle and precise guidance with cold gas thrusters might hit ITAR.