It might help a bit to get the antenna away from the body and elevated a bit more but it's nothing special. The times it's most dramatic is when the radio is buried deep in a pocket near the body, under a rifle the user is holding or if the user is a fat guy with fat rolls pushing against it. Moving the antenna six inches from the body will dramatically improve performance in any low signal situation.You can do the same thing with the radio in a pouch up high and it will probably work a bit better due to the more proper ground plane the radio provides with the antenna mounted right at it along with a clearer 360 degree view from the antenna.
The device in the picture is marketed to the AN/PRC-148 and 152. Literally no antenna will work well across the range of those radios 30-512. Physics won't allow for it. The antennas they use are a compromise. They have small transformer and resistive networks in the base to keep the SWR under control but that results in even more loss. Add in the lack of a proper ground plane and it's amazing they work at all. The use of a handset helps more than anything due to the wire of the microphone acting as a counterpoise on the lower bands. At least, that's what I've experienced.