I don't think it worked out. The advantages were supposed to be low launch and recovery speeds, the holy grail of carrier aviation, combined with low spot factor. The planform can be described as a very low aspect ratio flying wing. So, I would think it has the irritating features of that genre. One of those irritations is that you can not balance the pitching moments that high lift flaps give, so there aren't any. The prop slipstream was supposed to compensate by blowing higher speed air over the surface, but half of that is wasted because the prop disc extends outboard of the "wing tip". The net result would be that it would need more wing area to slow down to the quoted speeds. That generally affects the top speed and range/payload negatively, which is reflected in the higher empty and gross weights of the XF5-U compared to contemporaries. My guess was that they were counting on the vertical component of the thrust to help lift the plane. Another irritation of low aspect ratio is that you need higher angles of attack to achieve the same lift for a given wing area (the Cl alpha is small). Consequently, the nose needs to be pointed up higher than a conventional set-up when you slow down (or pull g's). That fact kind of synergizes with pointing the thrust line up. It all means you must have a much higher pilot eye position to view over the nose, which also produces aero drag because of the shapes you need to fair in the canopy. The taller canopy requires taller fins to compensate. With a conventional wing/tail layout, if you miss your approach speeds by a few knots you can use some tricks like extending the span and going to more elaborate flaps. These mods are expensive and increase empty weight but they do not screw up the rest of the airplane everyone has been working on. You have options in the "end game" of the design when optimistic weight estimates are killing you. Extend the span a couple feet, add a leading edge device and a couple more degrees of flap, extend the chord on the horizontal tail and you're there. On a flying wing, frequently you paint yourself into a corner whereby every pound increase in empty weight adds knots and there is nothing you can do about it except start over. You can't increase the wing area because it was the first line on the paper, so basic it affects every detail of the design. You can't modify the high lift system since it doesn't have one (OK, maybe there are some concepts but none successful to date). Up and away maneuvering can not be enhanced by those big props and gearboxes at the wing tips. Fighter handling qualities are bound to be unusual from the gyrospcopic effects alone, much less the prop swirl and all that jazz. The short story is that a judgement was made that there were too many problems to solve just to get it up to state-of-the-art propeller plane performance. By that time they wanted jets, which were a whole new set of problems.
As far as substituting this configuration for a tiltrotor, that is interesting. It would need more power and different flight controls (cyclic on the props) to hover and then it would be pointing straight up like a tailsitter. Also, if you tried to adapt this configuration to trash hauling it would reveal another irritating feature of flying wings. They have severe "packaging" problems that screw up the internal structure. Basically the equipment is so spread out, the top or bottom of the aircraft is all doors which is a challenge for the structural arranger. It would end up with a nice fuselage pod, more span, a proper tail...probably a tilt wing. No, I would not be a champion of this configuration.
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"Who cares if it works? Does it look good on the ramp?"
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