I'm not sure which brand I got, but while mine boosts the UHF range, it kills the VHF range. I went back to the regular 'rubber ducky'. Not much UHF action around here anyway.
I receive only, but the 2m/440mhz Larsen antenna definitely increases the received VHF signal on my Wouxun.
Also made up a rat-tail in case I transmit some day. A homemade version of this:
http://www.universal-radio.com/catalog/hamantht/2714.html