Maybe I'm missing something, but I find no easy or obvious way to do these actions in one command:

• remove non-tracked files from the working directory;
• checkout a specific revision;

If I compare with TortoiseHg, the action would be "purge" (which if my memory is correct is an optional extension of mercurial).
I often find useful to just clear the whole working directory from anything but the content of the checkout, with no untracked files and no uncommited changes.

For now I found ways to do something equivalent in SourceTree but the simplest way is to:
1. delete manually the content of the working directory but the .git directory;
2. use checkout in SourceTree but on a previous revision (because SourceTree don't allow re-checkouting the current revision if it's the head???) with the box checked for ignoring changes;
3. checkout again but the last revision this time.