UVB output from these bulbs is fantastic. As of right now, they're probably the best artificial source of UVA and UVB available! Usable UVB (although at low levels) is detectable 36"" away from the bulb! For most desert animals, I'd recommend Exo Terra's 70w SunRay or Zoo Med's Powdersun HID. You'll want the animals to primarily bask 12""-18"" away from the bulb. At that range, they'll get access to high quality UVB and the heat they need. Animals that prefer very high temperatures, such as many monitors, may require an additional source of heat. Halogen basking bulbs are great for this.
For those animals that require low to moderate levels of UVB, you have more options. The Zoo Med Powersun HID can be used, but you'll want the animal to be 24"" away from the bulb. The 50w and 35w Exo Terra SunRay bulbs are a much better option. I've had a couple pairs of Abronia graminea housed under 35w Sunrays (the bulb is about 6"" above the top of the enclosure), and they have been thriving, as well changing to an emerald green color. In captivity, A. graminea tend to turn turquoise or blue under insufficient UV lighting, so these animal's coloration speaks volumes about the quality of metal halide lighting.Keep in mind that UV does not penetrate glass, and only specialized acrylics allow for UV penetration. Screen can greatly reduce the amount of UVB that gets to your animals - the smaller the screen, the less UV passes through. Animals always need to be given ways to get out of (or away from) UV. Foliage, hides, branches, fake plants, and the like can all help make sure your animals do not get too much UV.