SourceTree is easy to download and easy to install but getting the security working can be a bit tricky to start with. This is made worse, if like me, you are pressed for time and sometimes behind an SSL aware man-in-the-middle firewall.
I kept getting an SSL certificate error when trying to clone a repository. I am fairly sure this is due to not adding the SSH public key to the repository on the web site but at the time I was in too much of a hurry.
As I was having trouble I did a quick bit of searching and found an option to 'Disable SSL certificate validation...'
That got rid of my errors and allowed me to get on and download my repository.
For my open source and experimental projects the security is not critical but for more important projects I would suggest taking the time to configure SSH correctly.