Totally agree on having a standard sub, my punto didn't come with one so I bought one of eBay for £12. It is very true that the sound is not as brilliant as that of a kenwood/alpine/mutant can produce, BUT here is the big BUT the sporting fiat sub fits so nice and snug in the wheel arch, totally out the way. In my case my boot is often filled with construction materials for my house, or filled to the rim with gathered wood for my wood burning stove. So a fancy sub and speaker enclosures built into boot will just get damaged and reduce my boot space!
I'm absolutely loving the sub though, I listen to a lot of dance/trance and r&b while driving and the sub is so freaking powerful my bass on the head-unit is set to -2