Ironically and contrary to the description, this plugin does in fact auto-activate. Upon installation, and going to Settings > Discussion, you'll find that both checkboxes are initially already checked, yet when looking at a post comment form, or bbPress reply form, neither have the quicktags bar visible.
There is definitely something wonky. I just did a test of all combinations of the two options.
bbPress checked, comments checked - quicktags visible on both (OK)
bbPress unchecked, comments checked - quicktags not visible on either (they should be visible on comments)
bbPress checked, comments unchecked - quicktags visible on both (they should only be visible on bbPress)
bbPress unchecked, comments unchecked - settings page reloads and now both options are checked and the quicktags are visible (should instead both be unchecked and quicktags should not be visible on either) -- you can't get it into a state of both being unchecked/disabled.
It's a very handy little plugin, though unusable for me in it's current form since it's impossible to get it into the state of having comment quicktags on, bbPress off. I hope to see it updated with these issues addressed.