A few Do335 were flying and it proved itself capable of outrunning the Tempest on the deck.
XF-5U was not a flying wing since it had a tail with elevators.
The flight test of the Ho-229 wasnt that bad at all, it flew very well:
The H.IX V2 reportedly displayed very good handling qualities, with only moderate lateral instability (a typical deficiency of tailless aircraft). While the second flight was equally successful, the undercarriage was damaged by a heavy landing caused by Ziller deploying the brake parachute too early during his landing approach. There are reports that during one of these test flights, the H.IX V2 undertook a simulated "dog-fight" with a Messerschmitt Me 262, the first operational jet fighter, and that the H.IX V2 outperformed the Me 262.
So with more time and Resources it might have been a factor to reccon with.