The Spectra is the farthest thing you can get from "low profile" or discrete! It is a monstrosity. And mine (on a mag mount) doesn't work any better than my stock rubber duck. Eighty bucks wasted, if you ask me.
Melvin, if "low profile" is your overriding concern, if the rubber duck won't do the job, and if for some reason you cannot go with a true undercover antenna (
http://www.sti-co.com/ ), then personally, I'd go with a glass mount, cellular look-alike scanner antenna, also available from Scanner Master. It works well in an urban or suburban environment (with relatively close system proximity), and it's about the closest thing you can get to "low profile" for surveillance work.