For a while there was a time when alien invasions were so common, yet so ineffectual, that armed commercial robots were fashionable to own. Combating death from the stars became a sort of pest control.
The Electro 500 was an entry level model, and distinguished from the 1000 series by having a more conventional armament loadout than the tachyon-pumped masers of the flagship model. While prestigious, the masers were unreliable in practice, and were often replaced with systems that were less expensive to maintain. Unmodified 1000s are collector's items, while 500's are still comparatively common.