EnTech is no longer selling the registered version of PowerStrip. You can still download the (unregistered) v.3.90
here.
I have been using it for a couple months now on my cab, and decided it was time to pay to remove the nag window on startup. I emailed the dev and was told, "I'm afraid this product is no longer available; it was discontinued at the beginning of the year."
When I asked if there was a replacement product or any way to unlock the registered version of powerstrip, I was told, "I'm afraid I'm not aware of either, and we no longer provide software of any kind to end users/consumers."
So I have no way of preventing the PowerStrip nag window from popping up every time I start my cab.