When a future customer knows that the product is good, it will increase your sales. And if there is a problem, it gives you a much better chance to fix it!
There are simply times that you need to see exactly what the customer is seeing, or you might need to help customers that are not as tech-savvy. This module is great for that! Saves so much time!
I've just tested the module on clean installation ps 1.7.6.7, and it works without any issues. My other users also reported that the module is working correctly on that version.
I believe you have some additional module installed on your system that prevents / blocks this one. Maybe some pretty-url, or something like that.