I have one, and I think it's pretty good for a 6.5" sub.
It won't give you the "boom" factor of a small box 10, 12, or 15, but it gives you bass unparalleled by any full ranger speaker/amp setup. The box size is really clutch, as I had a wedge box made for the reg. cab and I could still recline my seat all the way. It's just big enough to give bass to a reg. cab, particularly behind your seat. My only real complaint is that I wish I had the sub face the cab wall instead of the seat...you get a little deeper/louder bass if it's reflecting and radiating against a wall instead of facing you.
-1991 Ranger XLT 4X1 - DONATED
-3.0 V6 Auto, Regular Cab
Ford Ranger: Not supposed to be the best quality, just a cheap (to make) truck that fits the 1/4 ton niche. I only have one until I can afford a tacoma
7/19/07: got a tacoma