Yes. I own a Vortex Viper 6.5-20x-44mm, have a 3-9x 40mm Viper on order (clearance pricing!), and have handled a few examples of the low end Crossfire series. No hands on experience with the low-middle end Diamondback or the top end Razor series though. The Diamondbacks turrets appear to me to be very similar to the Nikon Buckmaster turrets. They're likely approximate in quality. Reviews online have listed them favorably against the Redfields, Elite 3200s and Burris Fullfield IIs at similar price points.
The Crossfires are bright and have great glass that is clear edge to edge, but their internals are suspect according to most reviews I've seen online. I've seen (relatively) a lot of failure reports. The examples I've handled were nice,but were also very new. I'm not sure I'd recommend a Crossfire.
On to Vipers:
Plusses: Glass on my Viper is extremely clear (fully multicoated with ED lenses), comparable to my dad's Bushnell 4200 and to my eyes slightly preferable to the Nikon Monarch 5-20x that I compared before buying the Viper. It's bright and clear out to the edges. There's also less tunnel vision than I get with Nikon scopes. Resolution is good enough to sometimes see .223 bullet holes at 300yds at 20x if the light conditions are extremely favorable.
The adjustments are very consistent. I can dial elevation from 100-300yds with no apparent loss of zero. I really like their resettable turret system and the click feel of the mechanism. Their side focus is pretty good, though it doesn't match up perfectly with range. The fast focus is handy, and the power ring arrangement is very easy to see while shooting prone.
Downsides: they don't have as forgiving of an eye box as the Monarch or a big eyebox scope such as most Leupolds. Eye relief is shortened to add more FOV, but is quite adequate for a .223 or .308.
Weight is also very high on my 30mm tube model, and it's still pretty high on the 1" model that I have coming to me. These are very sturdy scopes.
All in all, the compromises that Vortex took are more in the opposite direction from Leupold. If you like a lightweight scope with a big eyebox and long eye relief, then the Vortex Viper might not be your best bet. If resolution and very good turrets are what you're looking for, then the Viper might fit the bill.
