"Excellent"
I have a glass storage bottle which was proving very awkward to clean on the inside, saw this brush, thought I would give it a go. The brush is perfectly shaped and does exactly the job I wanted it to do, cleaning right down to the bottom and up the insides of the bottle. Just one pro tip - if, like mine the bottle has a narrow neck, the bristles will tend to "ping" open and spray water everywhere when you pull the brush out - just hold the bristles as you pull the brush out to prevent this happening!