As bad as that Cub flight looks in places, the odds of a fatal forced landing due to an engine out are low. Maybe not low enough for some, but certainly much lower than doing that in a Bonanza or Cirrus at more than double those speeds. However, if you are wanting to do a lot of this kind of low altitude flying, then having a redundant power system will be prudent even in a STOL plane.
I'm designing an ultralight that will have a redundant power system. It flies even slower than the Cub, but the pilot is not going to be as well protected. Maybe that is an even trade as far as risk of injury goes. The reason I wanted a redundant power system is that the intended use for an ultralight like I'm making means that I will be spending a large portion of my flying time within 200 feet of the ground. Most of the time, I expect to have limited landing options in the event of a complete power failure.
Ultralight engines have a significantly higher probability of experiencing a power failure than a Lycoming engine, and the multiple small engines I'm planning to use don't increase the cost beyond that of a single engine configuration. So, I feel that designing an ultralight with a redundant power system that can continue flying for extended durations after experiencing an engine failure is both prudent and cost-effective in my case.
PS - I wonder if that Cub pilot is smart enough to restrict that low altitude canyon flying to flights only going into the wind (and down the canyon, but that's for other safety reasons). If the engine were to quit on a flight like that, the difference in that Cub's impact energy between a forced landing into the trees with a 5 knot headwind vs. a 5 knot tail wind, will be significant.
