Stages Power meters have undergone a couple functional changes over the the years that represent an evolution of our product over time. The second generation design of the Stages Power Meter reflects a change in the plastic housing that covers the unit in order to further evolve our product into one that is slimmer, sleeker, and stronger. With this improvement, however, the basic electronics and function of the power meter remain the same. It also uses the same firmware and will continue to have the same ongoing firmware updates for improvements, added features, and bug fixes.
With the third iteration of the Stages Power meter (Stages Power L, Stages Power R, and Stages Power LR), the same sleek housing and robust battery door interface are retained, with the power meter featuring slightly redesigned electronics, providing improved accuracy, as well as adding an LED indicator light to the housing to show battery life and confirm that the power meter is awake.
If you're unclear which version of the product you currently own, please reference this image for a visual indicator of which housing style and placard image matches up with your power meter.