How do the small low profile omni mobile for VHF
and UHF compare in performance to conventional
1/4 wave (VHF) and 3 dB gain (UHF) antennas? I
have a hard time believing they are anything
close to comparable.

Antennex sells a VHF unity gain model
(TRABT-1420) and a UHF 3 dB gain model
(TRAB-4303). They also hold a patent on 'field
diverse' antenna technology.
http://www.antenex.com/pdfsandzips/megwhitepaper.pdf

I know these antennas are very popular for
public safety applications - does anyone have
real world A:B comparison data comparing them
with a conventional mobile antenna?

Thanks and 73,

Tad Danley, K3TD