The Viper is a low speed (6), over-stable, fairway driver that has a wicked fade (5). It’s great for curving around trees and other obstacles. It comes in the inexpensive DX plastic, and can be purchased for less than $10.
I’ve been using the Viper as more of a “mid range” disc, and use it for times when I want serious fade. My recommendation with the viper is to practice using it before you try tricky shots. The fade is much more than I anticipated, and I’ve put myself in some pretty awkward situations based on its greater than expected fade.
Despite the fact that I use it as a disc to get around trees, it actually can be thrown for some serious distance. According to the Summit Sports review below, it broke the world distance record three times (I’m guessing that was before disc technology got where it is now). If you’re a beginner/intermediate player, I’d recommend a more understable disc if you’re looking for more distance.