normal design with FBW -- no problem flying manually.
"relaxed stability design" with FBW (maybe F-16 was first, I'm not sure) -- flying is possible but very difficult with it off
"inherently unstable design" (probably includes latest US fighters F-22, JSF) -- cannot fly without FBW.
But the more unstable design can, IIRC, improve performance and allow dog fighting maneuvers that are simply impossible with conventional aircraft.
I'm not sure what, if any, the benefits of relaxed/no stability are for airliners. I doubt any airliners are inherently unstable yet (let the USAF/USN test for a decade first, I'd hope).
Tony
Who used to know more about this stuff