I would not even fool with the manufacturer that makes a claim like this.

That's what I was thinking, but what about the ratings tests from
Powerboat Reports and Practical Sailor. Are these reputable magazines?
Also, someone told me they have had good performance from a Maxrad
MHB5802 vhf antenna. It is the same type of antenna and claims 1/2
wave, 2.4db with ground plane and unity without ground plane. Would
this be a better choice? I know Maxrad is a more well known
manufacturer.