It must really depend on the guitar, with regard to the Black dog bridge, I think. Because I have one and have never found it to be overly bright (although I have heard other people say its bright!). Sure, there are plenty of high frequencies there (so it's definitely not dull sounding), but it has lots of low-mids and bass. I find it to be a really fat sounding pickup. It is true that there aren't lots of high mids, but I wonder if it really depends on the guitar - ie, if the guitar has a reasonable amount of high mids then it sounds great, but if the guitar is quite scooped in high-mids then you just get lots of highs and lows!! FWIW it's one of my favourite BKP's, throaty and fat, very open sounding with great note separation, etc.
Comparing it to the RY and Crawler bridges (I've had a crawler and still have a rebel yell too), the crawler is a bit darker and probably more balanced and 'even' over all frequencies, but to my ear that made it sound a bit characterless. The rebel yell is a much more 'shouty' pickup - lots more high mids and so much more cut to the sound, and a bit more compressed as its higher output than the BD. I would say the RY and BD are fairly similar in amounts of highs though, just very different in mid focus.
Just my thoughts :)
