I got a set of these feet from Wayne and tried them on my Scott Nixon TubeDac yesterday. It was quickly apparent that the top-end got more refined and the overall musical presentation became more coherent. A no-brainer for $16.50!
I am breaking in a new tube in my TubeDac right now (Amperex Orange Globe 6DJ8) so the extra refinement is much appreciated. While this tube has a much larger soundstage, better dynamics, better resolution and more extended frequency extremes than a Siemens 7308, the top end is still a bit rough at this stage of break-in.