Hasn't fucked up for me. Plus if it fucks up, the source drive is left alone and your target drive is what is being written on. All it's doing for source drive is reading it.
Once you get to the bigger drive you can either make the extra space part of that drive or partition it as a separate drive. It's your choice after that.
I bet if any other police force had this, that data would also be absolutely screwed. They're supposed to log who they pull over? Yeah that's not going to happen.