Purchasing a domain mapping upgrade for a free hosted WordPress.com blog for a single year does not make sense. I recommend that you do not purchase a domain mapping upgrade, unless you intend to blog over the long term and are committed to renewing your domain annually.
My recommendation is based on some facts I would like to share.
Failing to renew a domain mapping upgrade means every link to the domain URLs will be broken everywhere they appear throughout the internet.
Despite the fact the content will still be there under the .wordpress.com URLs it may take as long as 3-4 months for search engines to reindex them again under the .wordpress.com URLs.
Throughout those months anyone clicking the domain URLs to the posts, pages and media in the blog will experience a 404 (page not found).
What bloggers fail to understand when they do this nonsensical flash in the pan testing is that they are leaving a digital breadcrumb trail on the internet that can be followed for years to come. Leaving a trail of broken domain URLs behind when one is a student, who is playing around will not serve you well in the future so don’t do it!
Bottom line: Don’t purchase a domain mapping upgrade, unless you intend to blog over the long term and are committed to renewing your upgrade annually, prior to its expiration date.