The elementary school case would start by saying the first clue is that no one has heard of them or has owned one. That'll tell you they aren't very popular and therefore are less likely to be good. Another hint should be that they're only availible on e-bay, these kind of performance parts are almost always found in major retail, or at least online retail outlets.
But all if this is circumstantial and heresay, because no one has ever thought well enough about this product to purchase it, install it, and then tell the world how great it is. There are those out there with "magic power boxes" that think they're getting more hp, but no dyno has shown that. Even the relatively unknown Nology plug wire has dyno tests and time in pro race shops to back it up. The next tip should be the claimed hp increase, 3-5hp. A dyna or vortex cdi won't show you that, nor will replacement of any other electrical item on the machine.
If you want to be the guinea pig be my guest, as I said I wouldn't touch it unless I needed a replacement and even then I'd want a backup oem. There are lots of people who have the time/money to try these things first, if you're one of them then good luck.