I just picked up the similar version (3-15 x 50) used.
I was looking at it yesterday and comparing it to a Diamondback tactical that I picked up new on the cheap a while ago. I spent probably a half hour alternating between the two, looking at objects 1,300 yards to 95 yards away. I saw no discernible difference in the glass. Also on the DB Tactical, I can go from 4x to 16x and back again without having to touch the parallax adjustment. Same on an older Nikon Prostaff that I want the Vortex Razor HD LHT 3-15 to replace. On the Nikon I can go all the way up, down, or anywhere in between the 3.5x - 15x and not touch the parallax.
Unlike both of those, on the Razor, I have to change the parallax if I make a significant change in the magnification. If I stay within 3x - 8x, I don't need to touch anything. Once I get above 8x, have to adjust by what feels like a significant amount. The Razor is my first SFP, so maybe that's normal. I don't know. I emailed Vortex late yesterday, so waiting on their response.