It's all bull-crap. For one thing, it's supposed to be a "mobile" jammer, but with a Yagi antenna, you would have to physically track the receiver you wanted to jam - not very efficient. If the antenna was more omni-directional, you would need to increase the TX power to force all receivers in the unit's range into saturation. Also, this thing is illegal in most jusidictions.
If you really want to jam mobiles in your area (illegally, of course), a simple spark-gap transmitter is wideband enough to swamp 99% of all receivers in an area.