A buddy of mine has them and really likes them. We were both out scouting the other weekend, so I was able to spend some time behind them well. Spotted a few does at a hair over 500 yards. The sun was going down, she was in the shadows and lying down in the dirt. A pretty hard spot as she could easily be mistaken for a rock.
I have also spent quite a bit of time behind the Viper HD model as well (on scouting trips with a different friend).
As far as look and feel go, I feel the Leupold wins. Me personally, the Leupold just looks better overall and fit my hands better. Just felt more comfortable.
For glass quality, I personally felt the Leupold was brighter, sharper and just overall a better bino. The Leupold is on sale right now as well. I personally own the BX-5 15x56. I do own Vortex products too, so I am not one of those that only buys Leupold.
I know Vortex has their warranty, but so does Leupold and they will make it right should there be a problem. They have done so for me a few times and really went above and beyond.