One of the more ‘official’ clones of the Nelsonic Space Attacker came from Armitron with Martian Wars.
Available in a plastic/resin case with soft rubber front buttons, and side buttons on the extreme corners of the case, Martian Wars had a metal version but not badged as Armitron (it was branded as Tomy Watchman).
Like most clones, there is no music with this version, but the game beeps and the noises when changing modes/stopwatch are the same as the Nelsonic.
Gameplay and functions (other than the music) are the same as the Nelsonic. This may have been a forerunner (or released at about the same time) as the Star Trek Wrath of Khan version of the watch.