If they did work, I'm sure multi-billion dollar cell phone manufacturers would either include them with the phone, or they would integrate it into the phone.
If they spend millions on antenna designs, I'm sure they would use this if it works to improve reception. The people that buy these buy stuff like the Chop-0-Matic, believe in psychics, and think the Tooth Fairy should be elected as the head of the Department of Treasury. if you are going to waste your money on these, why not get something useful, like an ostrich buffer?