I dont' recall that I danced around it. I asked if the Calfee had a Formula disc and never heard back one way or the other. The reason I asked if it was a Formula was because it is one of the few hydraulic discs that has been marketed as a primary rear tandem disc brake. I did go on to comment that a hydraulic brake is a poor choice for a drag brake.
However, I would note that the Formula -- a hybrid, cable-actuated hydraulic disc -- is problematic in that it sometimes works well, but often times does not and has been a source of frustration for many of its owners. To keep one properly adjusted takes frequent tweaking and, in quite a few cases, the folks who purchased tandems with the Formula brakes have since retired the discs and retrofitted linear pull, cantilever or caliper brakes and as required added an Arai drag brake for touring, etc. On the bright side, with the exception of the first and perhaps second model years after introducing the Formula disc Santana outfitted its tandems with the correct fittings to work with some of these different configurations.
Rather than providing a bunch of hearsay, you can take a look at some of the comments that have been made for and against the Formula disc by some of the folks who own and/or sell and service them using this search string for the Tandem@Hobbes archives:
You can add additional search criteria, such as "AND problem" or "AND adjusting" to narrow down the search results from the 252 or so articles that will appear.
I have never owned a tandem with the Formula brake -- our Arriva was pre-disc -- but have ridden several tandems that did (Sovereign, Ti-700, Noventa and a Dual-Moto) in conjuction with making adjustments to them. Fortunately, during Santana's Asheville Tour in '98 Bill McCready gave a clinic on adjusting the Formula during Sunday's lunch stop which was far easier to understand than the "manual" that he wrote for it so I had a leg up on many owners/dealers who only had the manual: http://www.gtgtandems.com/tech/contents.html