Interesting that it states "..This antenna will help you to hear BOTH Sides of the conversation.. not just dispatch." as if one would have the input programmed, guess he's claiming it's a hot antenna. Never tried it to answer your question, but at $9.95, I've bought worse. You could always give it away to another user if it didnt work out.
Just looking at the size of the antenna, it appears to be a sleeve dipole design. It should be better than the rubber duck that comes on portable scanners.
Dude, I can build that thing for like $3. Its a freaking peice of PVC pipe, 2 end caps and most likeley a dipole or J-pole inside. Send me the parts and I will send you back an antenna.