Not exactly what I planned on doing today whilst sitting in the back of a car! Though whilst browsing these forums I bumbed into this thread and have kicked it off on my iPad with a bbPress test site importing from 30,000 post PHPBB site, been running now for around 30 minutes.
I’ll add some follow ups on how the data Looks in bbPress when I have the right tools 
EDIT: ~90 minutes after above
After ~60 minutes I have stopped it and had a look at the WordPress tables with myphpadmin and I cannot see any new posts in ‘wp_posts’ or ‘wp_users’
Is the ‘PhpBB_Not_Complete’ import tool active? i.e. Should I see more than nothing, nil, null as a result of trying this?
Cheers,
Stephen