Unsure how to use return values of method expansions

https://gitlab.redox-os.org/redox-os/ion/blob/master/manual/src/expansions/05-method.md contains only examples involving "echo", which IMHO should be considered an issue on its own.

the given exmple

echo $ends_with("FOOBAR" "BAR")

gives 1 as documented ; but doing

$ends_with("FOOBAR" "BAR") && echo ok || echo ko

gives

ion: bg [1] 27481
ion: command not found: 1
ion: ([1] 27481) exited with 0