The main advantages of the module is:
Checkout on a single page above the fold
Easy installation - just upload files and you are done
Full support for registration (creating new account, logging in)
Disable fields like fax, company, telephone, region, city, zip
Set a default shipping and payment method
Enable checkbox for newsletter subscription, terms and conditions
Allow customer to enter a comment for the order
Easily modify CSS / layout with regular Magento templates and CSS file
Change checkout title and description from administration interface
Auto-update prices and totals when choosing shipping/payment method
Auto-update available shipping rates when user chooses country, zip code or region
Auto-update available payment methods when user chooses shipping method
Allow gift messages for the order
Auto-detect users country by its IP
Its 100% open source!
You can see this module in action at the medkit.fi