AJAX Shopping Cart

Yes, this shopping cart module is mobile-friendly, so it will work fine on smartphones and tablets....

Yes, sure, Magento AJAX Cart allows you to add to cart from category page. Your clients will be able to add products and configure their settings right on a category page. This is done in a pop-up window to ensure seamless user experience....

Yes, you can add this option. Please navigate to System > Configuration > AJAX Cart > General Settings and set “Allow to change product quantity in confirmation dialog” to Yes:
...

No, our extension doesn't work with the up-sells at the moment. However, it's possible to display related products in the ajax window boosts sales, as you offer matching items to a targeted buyer. This will help you to increase the average order valu...

Yes, of course. You can choose how the pop-up window should look like by changing colors of its elements. This can be done in System > Configuration > AJAX Cart > Visual Options:
...

Yes, you can choose a preferable variant in System > Configuration > AJAX Cart > General Settings:
...