I have to agree with Jacky. You have an opportunity here since there is not a GUI tool currently available that can enforce the git-flow model.
"... the issue is that it cannot be enforced in a Git GUI, only on the command line ..."
I know a few developers that are very uncomfortable at the cli and would like a GUI like SourceTree with git-flow support. If it could simplify there work flow.
"For teams that have to do formal releases on a longer term interval (a few weeks to a few months between releases), and be able to do hot-fixes and maintenance branches and other things that arise from shipping so infrequently, git-flow makes sense and I would highly advocate it’s use."
just my $0.02