What is your goal with them? They don't really make the sound, though whatever they are attached to or in contact with might vibrate and make some annoying noises.
If you want to feel your body shake like you have a 15" sub under your butt while you're driving, then I guess they'd be an OK option. Devices like this are good for theme park rides to add realism (like the Days of Thunder "ride"), or in theater systems to augment movement of things on screen with extreme low frequency vibrations that transfer across devices, to add a bit more realism. But for musical applications, I see no actual use for them.
I saw them used in an audio build on here a while ago with two 10" subs behind the seat. A little overkill in my opinion, but whatever floats your boat.
Back in the day my buddy had some mounted to the floor under the seat in his Nissan Hardbody. I was so surprised how much it added to the light system he had. I don't know if it will work the same on the Fiero because all the plactic may mute the sound. And yes it add sound in the cab of that truck.
I haven't used them before so I don't know what real effect they have. I know they are said to only create a tactile feeling, so they don't reproduce sound they just vibrate what they are connected to. Having said that, I do have 2 Aura force amplifiers in my Neon. They are built very well and sound great, so I would suspect whatever those shakers do that they would do it well.
