The brushes are perfect for applying rustbuster fluid, the fluid can be scrubbed into tight corners and seams. I didn't do the repair above, it's an old repair which I tidied up and applied the rust fluid.

 

They can scrub out tight corners and clean electrical items. 

 

This brush later applied seam sealer to a repair which I did do,

and it worked well. I would say get a couple every time you're in Tescos, they are very useful.