I would like to add more, if you do not use Aspose.Cells component with (valid) license file (or do not set/use the licensing code in your project, it will be called a demo/evaluation version. The download link is same for all the users: http://www.aspose.com/community/files/51/.net-components/aspose.cells-for-.net/entry207989.aspx
Well, the evaluation version of Aspose.Cells product (product without a valid license (temporary or permanent) specified) provides partial product functionality, it is limited to open/generate 100 files in one program and an extra worksheet with evaluation watermark. Secondly it may not provide you the feasibility to use all the APIs the product can support. But there is no limitation upon evaluation, you may use the product without the valid license as long as you wish.
Moreover, when you subscribe or when you purchase the license for the product, you are eligible to use versions / bug fixes of the products that are released in the next whole year as free.
Have a good day!
Feel free to contact us anytime if you need further info.