They're designed similarly to an upright cycle, with a saddle seat and pedals positioned vertically underneath the seat, but instead of automated resistance levels, you manually adjust the resistance yourself.
Darren Rowse, creator of the ProBlogger.net website, enumerates many reasons to avoid all automated blogging tools (in fact, he also recommends against using any automated social media software, including Twitter clients).
While they seem to offer more services, some (such as one-way link building) are unethical by web standards, and others (such as RSS Syndication) are automated, one-click processes that really can't be called a "service".
Rowse also talks about how you run the risk of running afoul of copyright and other plagiarism laws since automated programs can't really ask permission to use content, and that can get you and your blogs in trouble.
Registration provides you with access to numerous features including the ability to review past statements and transactions, view current statements and activity and even set up automated or one time online payments.