Multiple physical knows will never fail all at once like a single touchscreen can. As a small plane pilot I prefer to have as many independent systems as possible; I use an iPad for instruments and navigation, but every single function is duplicated by a separate instrument, so if I lose the iPad for any reason I have the instruments in the cockpit. I had several incidents where single components failed, but I was able to safely land the plane every time. Hardware failures are as much as a problem as software failures and dual-redundant critical systems are far better than multi-functional devices.