My company uses Aha! and we're getting a ton out of it. Finally, we have a structured means of clearly communicating product strategy/objectives and demonstrating how it translates into truly necessary engineering effort.
It helps demonstrate that product management is not wizardry, it's a deductive process that can be open to everyone. In the case of a small startup, it seems like it could be an almost automated means of reassuring investors that the team is executing on-plan.
