This is a great plugin but the 'lite' version is limited and you will be strongly encouraged by the author to buy the 'premium' version when you ask for support. In fact, you will NEED the 'premium' version to do anything other than really basic stuff.
The 'premium' version (which, confusingly, has a different name) is inexpensive to purchase and works really well but is missing a few bits of core functionality (like merchant emails for the manual payment gateway, for example) and you will end up paying the author extra to supply the code unless you're pretty handy with PHP and SQL. That said, if you end up paying an extra $50 or so to get it fully functional it's still a reasonable buy.
The author (Niaz) is very friendly and replies promptly to support emails but often with requests for extra payment for code revisions or with slightly confused messages. So, patience is required but you should get there in the end!
Summary: The 'premium' version is a really fantastic, straightforward shopcart with plenty of functionality but you will have to be prepared for a bit of work and/or extra payment when needing modifications.