This particular example was laboriously built from scratch by PDH Enterprises to be as close an exact replica of the original Sten as possible. Some of the dimensions had to be slightly different from a genuine Sten in order to make the Home Office happy, so be careful buying new stocks etc for it, but it does take genuine 9mm Sten mags.
Included in the sale are FOUR genuine Sten magazines AND a genuine Sten magazine loading tool.
As with the original, this replica Sten fires in both semi auto and full auto. I would say it's probably less reliable than the original mostly due to how incredibly dirty the blank ammo runs when compared to 9mm ball. The amount of carbon build-up after two magazines is crazy, and I have never got through all four mags in succession without developing an extraction issue.
No licence is required to buy or own one of these, but a reasonable defence does need to be demonstrated. For example, being a member of a re-enactment group.