So right now am using the coventional setup (incandencent bulb with reptisun 5.0 tube ) but I want to try out the powersun and am wondering how often to replace this bulb? Have users here had any luck with.this bulb?
I would stick with the 5.0 and the heat lamp setup. MV lamps are really meant for desert animals. The amount of UVB produced by these lamps is such that a UV meter would be a good tool to use when setting up the lamp so that you do not create more UVB in the basking spot than is needed. MV lamps produce about as much UVB as you'd find outside. But you must remember that chameleons don't bask in direct sunlight mid day. They like to bask in the morning and later in the afternoon when the sun is lower in the sky and UV levels are not so intense. During the day as they move around the trees and hunt they are exposed to lower levels of UVB, such as what you would find from a linear tube on a cage.
So I wouldn't by buying the MV lamp unless you plan to invest another $150 on a UVB meter.
To show off a UVB meter in use... here are a couple of pics I took while setting up my bearded dragon's cage.