You are correct about the Gel setup. A Gel Filter is kind of like thick colored cellophane. They are used for high powered stage lighting. They are hand cut to the same shape as a lens and are held in behind the lens using the lens itself and the mounting screws.
Unfortunately I don't have a decent camera or I would put better pictures up.

I'm not sure where you got $30 from but the Smoke goes for $20. Maybe you need to refresh you're the browser page cache?
Unless.... Ok. I know what you're looking at. The one with a $30 price is for a Smoke Lens with a Gel Filter permanently attached. If you want to be able to change them then you need to get a normal Smoke Lens ($20ea) from the "Buy Lens" page and then order the Gel Filters separately ($5ea.)from the "Buy Gel" page.

As far as the theft deterrent I got a high end stock stereo from the junkyard but the damn thing works perfectly and because of that I'm having a hard time bringing myself to hack it up to be a dummy display cover. Maybe I'll look for a broken one in the future.

Believe it or not I cracked my rib by putting in the Empegs sled in my Lincoln (now that it's finally running again) and leaning over the thigh bolsters on the passenger seat. I guess my doctors irritating nurse was right about smoking making you're bones brittle. I guess just the pressure of me leaning over it was enough to give it a hairline fracture.