No not at all. That is actually one area where TM is better than a clone because TM keeps versions of all file changes. So you could option key boot from the TM disk and erase your drive then restore back to a previous date in time. For example if you installed Yosemite today and decided you did not like it, you could restore back to yesterday's TM backup and have Mavericks.
TM does backup the entire OS along with apps and your data.
Unless you have a need to be able to boot and temporarily run from a cloned disk, there is no need for you to buy cloning software.