Hi Hester, I found the back pack thing a pest actually and I just ended up making up the mixture in a designated watering can and using it, it was quicker.
We inherited here a weed want of humungous proportions - its a calor gas bottle on a wheelie thing with a big wand attached to it. Much more of an industrial scale than a domestic version and you just torch everything in site.
We're just about to lay a large gravel area and it's a must have I'd say.