The former has a 60°×60° FOV, to sense X-ray flashes,
and the latter, 1°×1°.
Note that other astronomy-related observatory-concepts, space and ground,
have been named for Einstein, among them another X-ray space observatory:
the c1980 NASA satellite HEAO-2 also went by the name
Einstein Observatory. Also, a current concept for a future ground
gravitational-wave detector is named the Einstein Telescope.