It's really about how you and your team are different in the end. Yes, there is always that risk...it is just how things work in the startup world. No one is signing NDAs and your enhanced feature has likely been thought of by others. It is better to try and get your product / feature out into the world than hold it for fear of being poached by the big guys....they likely have bigger problems and opportunities to worry about. Take reasonable precautions and go for it.