I have tried both the Inifity Basslink I and II. The "I" was in both a friend's silverado extended cab and then in an ex-girlfriend's trunk of a hyundai elantra. The Basslink I didn't impress me that much, but was better than nothing and was nice and small. That was the goal for both of their systems.....add some bottom end, but maintain storage space.
The Basslink II I just got for the trunk of my g/f's car (Acura 3.2 CL Type S). It fit in the drivers' side rear storage area almost like it was made for the car and looks almost like it was meant to be there from the factory. She already has a bose system from the factory and it has an external factory amp. Stock Bose 6.5's in the doors and 6x9's in the rear deck. They sound good, but lack in the low bass department.
I want to let you know that I am more than happy with the basslink II in her car. I previously had a TC Sounds TC 1000 10" ported in the trunk off of 500 watts rms. It sounded good, but took up too much space and she wouldn't quit nagging about that. I sold the sub to a friend for his home theater (and he is happy with it) and she likes the basslink II.
I realize that you can make better setups in small spaces, but for $100 for this setup is a pretty nice deal. The Basslink II is supposed to use a square woofer and passive radiator vs. round to get more cone area than the basslink I and is also 250 watts rms vs. the 200 watts rms of the basslink I. Those two things sound like they don't make much of a difference, but I want to let you know that I am quite impressed with the 2nd version.
I do know what good bass is, as I have a 21" Incriminator Audio Death Penalty in my Navigator. Just wanted to give you folks a heads up!