Transparent Battery Widget at work in portrait (second widget from the top in the right-hand image)
This simplicity of function is in contrast to applications like Nokia Battery Monitor and qooBattery. Both of those applications provide more detailed information about your power usage, such as voltage charts and power usage by application. Transparent Battery Widget offers none of that, even though it costs as much as qooBattery.
Given that the main functionality of Transparent Battery Widget is to change its colours, it would seem that the driving reason to pick this above the alternatives is if you prefer how it looks. If you are more detail orientated, then Nokia Battery Monitor or qooBattery will be better options.