It's the ideal product to manage, right? A product that you, the product manager, are the ideal customer. Immediately, your workload is cut in half because you can validate your own requirements, your own messaging, and your own positioning. It's a product for you, after all.
Of course, this couldn't be further from the truth. The reality is that if you are managing a product for which you are the ideal customer, you need to be extra careful to ensure your own personal biases and assumptions are not polluting your product.
When you start hearing yourself thinking, "Yes, this would make my work so much easier," or, "No, I would never use that kind of feature," you need to get out and start talking to your market to validate that it would make their work easier and that they would never use that feature.
Otherwise, you may wind up building a product for which you are the only customer.