I have a decent amount of experience with bass shakers, so I'll share. First I used two of them in my home theater. Amazing experience. I had 100 watts available for each of the normal ones (25 rms each). I secured them tightly to the bottom of my futon (I'm in college, so no real couch...) and crossed them at around 80 hz, with the sub. They added amazing rumble during movies, especially explosions and stuff.
I ran them full range ones just for fun...voices coming from a futon is pretty freaky, I'll tell you that.
I had to do a lot of moving, so I decided to install them in my car instead. I screwed them extremely tightly to the floor pan of my car and cut off the bottoms of the screws and sprayed underbody coating underneath to prevent rusting.
I am running mine off of a cheap walmart amp that supposedly puts out 150 watts rms at 4 ohms...I'm running my two in series so should get about 38 watts rms on each one. Mine can handle 25 watts, like I already said.
The ones you linked to can handle 50. The actual only difference between mine and those is the heat sinks. The internals are identical. So you won't have to worry about heat buildup, just make sure you don't bottom them out.
Secure them down very very very tight. You want all of the rumble to transfer to the vehicle.
Don't put them on the seat, you will be able to localize it completely and it will feel stupid. Instead, put them on the floorpan like I did. It will give you a rumble over a broader area, and less localizable. Unless I tell someone or show them I have them, they just think it's my single 12" 300 watt rms sub that is rumbling the interior of the car.
Make sure you lowpass them at like 60-70 hz, or even less. If you cross them too high, you will feel high frequencies too much, and it will feel like buzzing. Not a good feeling.
Don't push them too hard and make them stand out. They should blend with your sub. I often forget I even have them in my car. Remember to play with phase, because these could cancel or, or enhance, the rumble from your sub.
Was it worth it for me? Definitely. I paid $40 for my pair and got the amp for free.
What sub setup do you have right now?