I have an OS 160 FX mounted on my Dave Patrick Ultimate. I have heard that the firewalls tend to come off these planes, so I've been watching it closely. Compared to my Ultimate, the Hangar 9 Edge is a TANK! I don't use a soft mount, nor do I feel it needs one, even on a very light plane like this one. On the Edge, there's absolutely no reason to add the additional weight or complexity of a soft mount, not to mention that you're never going to be able to use a muffler with a soft mount. With a tuned pipe, headers are a problem, a Pitts style muffler on a soft mount will probably last less than a half dozen flights!