50-GENK51A vs 50-GENK50A

What is the different between the 50-GENK51A and the 50-GENK50A. As far as I can tell, they are the same, yet the 51A is $50 less. Also, any idea what the mount is for the Prius? I'm not sure if I need to order another one or not.

Yes, I've read the warnings about improper installations interfering with the side-curtain airbag. I'm not concerned with this. I'm comfortable with the installation process.

 

Yes, I saw that site. So, the 50A's wiring harness is $50? I'm not sure that's worth it. It would only save me a few minutes, and that's assuming the wires I need are even present into the stock plug on my Prius.

I was just trying to figure out if there was more to it or not.

Any idea if there is a special mount for the windshield? It's not clear from what I've read, because the Prius is never listed with the other Toyotas.