I can't speak for the Crunch Box but I do use a Brownie on a Twin Reverb and Les Paul and it sounds great. I am not a fan of distortion units throught the Twin because, for lack of a better term, they sound fake. As the above post states, the Brownie sounds more natural to me.
Different animals IMHO. The Brownie is a FET based pedal and the Crunch Box is diode clipper. I have owned both in the past and they are both excellent pedals for the price of the admission. I personally preferred the Brownie. Being a FET it was less congested and compressed sounding than the CB. The amount of OD was similar, but the clarity of the Brownie won me over. If possible, I would find both used and then make your decision on whiich is best for your needs.
Unless you're looking for an 80's JCM800 type of sound with some fizz when the gain is dimed, I would take the Brownie. The Brownie has more of a natural plexi type of sound going for it. Mine had two type of transistors that you could swap. One for low gain, and the other for high gain.
After re-checking the demos I had heard before, the Brownie does indeed sound to me more natural and more like an amp-
I'll be going for the Brownie. Not really into Van Halen per se, but looking for something in addition to my three dirts (vintage EHX Hot Tubes, DST Fat Acid and OceanEFX Pearl Drive) other than yet another "overdrive".