No experience with the Viper spotting scope but the Viper riflescopes that I have used have been fantastic, especially for the money.
I had the money and wanted a spotter that I could use for the rest of my life and pass on to my son-in-law, or grandson (when the time eventually comes for either; two very young girls at home) so I bought a Razor spotting scope. "Amazing" is a good word to describe that one.
If money is an issue, the Konus spotting scopes are a real bargain. One of my buddies has one and I was genuinely impressed. That said, I've not heard good things about Konus customer service with regard to warranty work, while I can say that my Razor went in for work (fleck of dirt on the prism) with no RA or any other drama or approval and was serviced, inspected, repurged and returned to factory new condition and was back in my hands 6 days after they received it. 4 days of that were transit and the other two were a weekend.