Hi
They're excellent for working off ladders, cleaning dust, cobwebs etc. off walls, ledges and rough uneven surfaces. You can maintain safe working practice with two feet and one hand on the ladder and still use it easily. We regularly clean a chapel, working at height with lots of old oak timbers, ragstone inside walls and high vaulted ceiling.
In smaller enclosed spaces they can bump around a bit until you're accustomed to having one on your back. I would recommend them. Check out the vac motor power too when you decide to buy.
Grant