Hooked up my Dr Z Brake Lite last night. Well impressed!
It didn't suck tone at all, and even at the highest setting -11db, it was very responsive.
I love the DC30 running at full power, also at the level of just beaking up a tiny bit, and the Dr Z Brake Lite has brought my volume down beautifully but kept the responsiveness I love at the 30W setting.
I'm hearing more and more good responses about the Brake Lite, and best of all, it screws into the inside of my combo with two screws.
They also make a Brake Lite SA (stand alone) for those who are running a head and cab setup. At $169, it's a winner.

I use one on my Dizzy 30 all the time. It sounds great and makes the amp very usable at low volume. A word of warning though... it will eat your power tubes. It seems to dramatically reduce the life of the power tubes.