There are so many variations of Linux out there, and I've never used one that wasn't downloadable for free. I have some flavor of Linux running on every machine that I use, and I've never messed up the host system.
Trying Linux on a spare laptop seems like a better idea than playing with with Ubuntu on your daily driver. About the only way I could imagine messing up the host system, is deleting some files, which you would have to do on purpose.
You wouldn't be trying to put the shuck on me, would ya stranger?
As I often get told, step aside son, you're a blockin' the MOMO!