White dolphin has the same thing. I've given it a lot of thought:
-good: lots of water (when we weekend, its really nice)
-bad: when tanks are anything close to full, boat lists to port (we compensate by storing everything with any weight on starbard side) Of course the extra weight is not fast, but you can always just run the water before race.
-bad: the 2nd tank blocks the drain hole that most folks run the auto bilge pump hose out. there are no good options for running hose out the starboard side, so i am still w/o an auto pump
-bad: less storage (but we dont miss it)
Overall - I like the tanks (nothing beats a hot shower at anchor in the winter).
-dan
