Pros: Deep, Rich Bass, Unbelieveable Sound, Unique Design
Cons: The impedance is a little misleading, but nothing catastrophic, otherwise ABSOLUTELY NOTHING!
The bottom line: The Solo-Baric is certainly a top-end piece of equipment that will deliver what you need, provided it is set up correctly.
After long, hard research, I purchased the Solo-Baric S12L7 4 ohm. I should mention that my family have been doing car audio modifications for over 30 years, and growing up in that environment gave me the knowledge I needed to understand what type of sound I was trying to achieve in my vehicle and how I could best achieve it. I had been planning my car stereo for close to a year before I finally began purchasing my equipment. The sound was generally shooting for was not so much loud as DEEP. There are so many cars with systems that can play at incredible volumes, but very low bass notes come out shallow and tend to disappoint me. Therefore, I looked into the Solo-baric.
The first thing I looked into was the claim that the Solo-baric's square shape provided more sound than normal. Before hearing it I concluded that this was true because the square has more area than the circle 12'' woofer, therefore more of the woofer moves and more sound is produced. I also read that these woofers go down to 20 hz. This did not quite reach the depth that I wished to achieve, but I decided to settle for it and stay with Kicker.

When setting up my system, I faced one issue with the Solo-baric. The fact that it is dual voice coil changes the impedance!!!This is extremely IMPORTANT for anyone considering purchasing a Solo-baric. The 4 ohm woofer can either be wired to a 2 ohm or an 8 ohm load. Since I've never seen an 8 ohm amp with enough power to handle a Solo-baric, I naturally wired it for 2 ohms. The enclosure I put it in is large enough to accomodate 2 Solo-barics, it fills a large space in my trunk. I should also mention that I have a 2005 Nissan Altima. While I was told that this is a waste of space, I opted for the large box size because of a general rule I learned: The bigger the enclosure (in cubic feet) the bigger the sound. Long story short, I wired the Solo-baric to a Kenwood 9152-D mono amp (900 RMS) and through a 1.2F capacitor. I should also emphasize that I did NOT change the head unit, the stock head unit for the Altima is what is in the car right now.
The result.....My Solo-baric sounds like even more than a 12'', even more than a 15''...It has a very unique crispness to it. Of course, the Kenwood amplifier has a LOT to do with it, I'm sure it would not have sounded NEARLY as good with a low quality amplifier. I spent $200 on my Solo-baric and $170 on my amp, and this current setup provides high level bass. My cousin spent a little over $1200 on his Galant's audio system, where he put in not one but TWO Rockford Fosgate amps, a Kenwood head unit, and a PAIR of JL Audio subs, and was REAL P.O'd at me when my one Solo-baric and one amp blew his bass away. A car subwoofer is probably one of the most difficult things to rate and review for other people, mainly because the setup is the deciding factor in how your system will sound. Overall, I love my Solo-baric, and it sounds great....but this is especially because I set it up correctly. I have seen Solo-barics tear from distortion because their owners did not set the system up correctly and tried to achieve a sound greater than their setup allowed. If you know what you are doing, or if you are having your system professionally done, then I highly praise and recommend the Solo-baric 12'' to you. Just be sure to take into account the issue with the dual voice coil impedance I mentioned earlier.