Does anyone have any personal experience with this SEO:

9L4 - Power supply, 12 volt (MSRP = $168.00)
12 volt direct power supply from the battery with two separate 30 amp fused circuits. Each circuit has a 30 amp mini fuse for both positive and ground to protect electrical accessories. Main supply lead has a 40 amp maxi-fuse. All fuses are serviceable. Provides either direct battery power or operation through the ignition system. Hook-up wire is provided under the passenger side glove box. Operational amperage is 21 amps each circuit; 28 amps total. Hook-up and operational instructions are provided.

In particular, does it save enough hassle be worth it?
It looks like it might eliminate having to poke another hole in the firewall to get additional power into the cab...

I have no idea what exactly that is, but to me it ain't worth 168 dollars for some wire and a couple of fuses. I'd just get standard off the shelf parts and do the work myself save about $100.

Yep, I agree.
As long as there's a good place to penetrate the firewall that doesn't leak.