I bought one, just cause I needed something for under the cd player...I rarely use it, and its not that great when I do use it. It only increases db over a preselected frequency (normally set up on the amp). Mine looks cool as hell though....so I cant complain.
Digital voltmeter on the left, and bass boost on the right.
I have a indash crossover that has gain control over my sub amp and it does come in handy. I have found that some music is lacking on the low end and turning the gain up helps.
I had 2 10's installed in my dad's truck and the amp that is pushing them has a bass knob, I personally like having it. When i drive my dad's truck i can turn up the bass, and when he drives his truck he can turn the bass down. I like the fact that theres no need to mess with the amp, which is under the seat, to adjust the bass.
Had one with my autotek amp in my beater. I liked being able to adjust the volume on the amp from the front. Allows you to quickly turn it up if the song needs more, or turn it down if you've had enough.
I just got my Kenwood amp installed today and it came with a remote knob. its actually nice to have. I can adjust the bass to the different types of music I listen to.
My Rockford has one, and I absolutely love it. I don't think I would go any other way. I actually mounted mine inside the center console so its hidden and looks great.
i hate needing to have one in my truck. my rockford amp will only run at 60% without it (you can actually hear the differance). so mine is plugged in, and dropped behind the amp rack. i never touch the thing. to me they are completely pointless. but that is just my oppinion.
I have both a Bass Boost knob off my rockford, and an Epicenter control. I use both of them since I change what musci I listen too from rock / rap / techno/ and even classical.
Being able to change the amount of Bass is great! IMHO.