mattia - 5:03 pm on Oct 19, 2011 (gmt 0)
Hosted solution carts do not let customer alter the code source of the cart. It is a well known fact that customers using this kind of solution accept. If you were able to modify the code source of their cart, then they wouldn't be able to support you anymore.
That said, it looks like they have nice templates and a complete list of all standard ecommerce features, so you should be OK with not having to have to build a new one.
I like the fact that they give you a free SSL certificate, but I hope it is not a shared one.