Zero experience with it. I did go down to the Race Shop to ask around and I got my first look at one at the same time. A lot smaller than I thought. The word from the guys down there was that internal mounts can sometimes result in spotty performance, but it's definitely a YMMV thing. Along those lines,
this link has an interesting internal method...though the shape of the SC toptube might encourage it to walk it's way forward vs staying in place. If it's a wall thickness thing causing signal dropouts on internal installations the downtube might be a slightly better candidate than toptube as well.
Carl Matson