You'll find that in business, companies do talk about "units" or "items" to describe their production capacity. So a company making smoke detectors might say eg that it produced 500,000 units per year. Click
here for an example from the automobile industry which says that the carmaker Bentley is aiming to sell 1,000 units annually to China. 1 unit = 1 product so in this case, 1,000 cars.
Here an example with "items" :
Production Network Benetton's manufacturing operations are based on its own factories ... It is responsible for producing around 20 million items per year.
So either would be fine.