What is "good" for a battery light is very subjective - max brightness, consistent, optics, beam pattern, battery life, modes, features, recharging options, etc.
Now owning, and having tried, a number of battery powered bike lights I am realizing that optics is a very important feature. Throwing less light but exactly where its needed will be more efficient then a light that throws more light but "wastes" it in one spot or in places its not needed, like up high (for road riding at least).
But optics isn't just about a beam shape with a good cutoff. It is width of beam, even spread of light without hot spots, etc. I have seen lights with good optics but lower lumens more effective then lights with higher lumens but poor optics.
I haven't used a B&M light personally, but would like to move to one (or something with similar optical quality) in the future from the research I have done (likely with a dynamo setup but not because I am anti-battery lights, as to date I only have battery lights).