Drybrushing is seldom a good idea on a miniature but it does work wonders for weathering buildings and terrain. I picked these two brushes up a few months ago and they've served very well at their intended purpose (unlike the other Citadel brushes, which are pretty rubbish).
I've also discovered a few other unexpected uses for them. Because drybrushing is tough job for a brush - life expectancy is rather short - I don't really mind what these get used for.
As a result I started using them to hook paint out of the pots and onto my pallet. They're really useful for this as they'll take a reasonable load without clogging up the ferrule, which can be a sod to clean. Both are also useful for applying thinned base coats, delivering the paint very quickly and effectively on a batch job, like my Blood Bowl Orcs. As with all the Citadel brushes it's hard to recommend these, although they have come in rather handy.