I purchased the Knowledge OTG to try out after sending back a Smith IOX Elite Turbofan for repair.
The Knowledge is a decent OTG fan goggle and will keep the fog off but the fan noise is noticeable, the lens is not near the quality of the IOX (or Phenom or Prophecy as I understand) and lens choice is limited if you want to swap or buy additional lenses.
If you are looking for a standard OTG goggle that will help keep your glasses fog free - the Knowledge should do the trick. And hopefully you can find it at a deep discount. But for the same price at retail, the IOX without the fan might work just as well, and is hands down a better goggle.