Lastly, I weighed both scopes. The Helos had a bubble level and scope caps on. It weighed about 2 pounds:
The Vortex weighed in at about 1.5 pounds (no caps or level installed):
There is a definite and pronounced weight difference. The Helos really is a solid piece of gear.
Another real practical difference between the two scopes is that the reticle subtensions on the Helos are about twice as thick as those on the Vortex.
All that said, the glass quality seems to be comparable and both track and work well. The Helos has more features - illuminated reticle, lockable turrets, magnification ring knob, larger elevation and windage knobs. It also feels more "solid". It retails at about $525-$550.
The Vortex is lighter, has crisper "clicks", thinner reticle, easier operation (windage and elevation directions clearly marked from behind) and smoother magnification operation. The reticle layouts are practically the same except the Vortex EBR-2C has no center crosshair, it has a void. It retails at about $400-$425.
If I had to choose between the two on a rimfire (and I do), I'd probably (and will) choose the Vortex. This is mainly due to 3 factors. First, the Vortex reticle being thinner is a big deal for me. Second, the Vortex knobs and rings turn much crisper, easier and smoother. And third, the Vortex is $100-$150 cheaper.
For a centerfire rifle, notwithstanding the price difference, I am not as certain I would pick the Diamondback over the Helos. The reticle thickness is not as much an issue with larger calibers, I wouldn't think. I also definitely think the Helos will withstand heavy recoil without issue because it really is built like a tank. The Diamondback may well hold up to recoil over time, but it is still too new a product to really know yet. I think it will, but time will tell. That being said, for serious long range or competition use, I think if I was gonna go with a Vortex product (other than a Razor, obviously), I would go with a Viper PST over the Diamondback, if only for the known performance and hard zero stop.