This is quoted from 'Aircraft of the Luftwaffe 1935-1945' by Jean-Denis G.G. Lepage (2009) and is the only real text I have found in my references. With such a rare subject more detailed info may be hard to find.
Heinkel He 280
"The single-seat, two-jet-engine fighter
Heinkel He 280 was a remarkable achievement
designed by engineer Max Müller from the
Jumo Company. The second Heinkel jet aircraft
had a span of 12 m (39 ft 5 in), a length
of 10.20 m (33 ft 5.5 in), a height of 3.19 m (10
ft 6 in) and an empty weight of 3,350 kg (7,386
lbs). It had twin fins and retractable tricycle
landing gear, and was powered by two Junkers
Jumo 004A turbojets mounted under the wings
which gave a maximum speed of 817
km/h (508 mph) and a range of 615 km (382
miles). Intended armament was three 20-mm
MG 151 cannons, and a bomb load of 500 kg
(1,102 lbs) for the envisioned He 280B fighter/
bomber version. The prototype He 280 V1
made its first flight in April 1941, and proved
its excellent maneuverability and tremendous
potential during a mock dogfight with a Focke-
Wulf 190 in early 1942 which the He 280 easily
won. Yet this attractive and advanced craft
appeared at a time when the German leadership
showed no interest in jet aircraft or any
novelty that could not be used at once for a
short Blitzkrieg campaign. The aircraft was
plagued with engine troubles, but there are
suggestions that the decision to reject the He
280 was political. In any case, the Heinkel
project was abandoned in favor of the Messerschmitt
Me 262. Only nine prototypes were
built and used in a variety of test flights which
greatly contributed to turbojet-powered-aircraft
research."