Should sound very good, you will probably need at least a single farad capacitor so you do not have the dimming of the lights when the amp draws big power, but it is cheap. It is harder to find a place to mount the thing than purchase it.

I would HGHLY recommend another set of components in the factory rear spot, with custom mounted tweets for imaging. That 12" is going to be a lot louder in that car than you think...

I have never used the OEM amp, but it must have a crossover in it to control the factory subs, you will lose that when you remove it, so unless your new amp has an independent X-over for each channel, you will need an inline X-over if you do not replace the factory subs...