The Sten Gun earned a reputation for being cheap and shoddy, but trials showed that it wasn't all that bad.
Seems acceptable. Let's compare it with the results of Soviet submachinegun trials. The numbers will be a little off, since the British were firing at 91.4 meters instead of 100, and taking the line from the center of the rectangle to the corner will (in most cases) result in an R100 that is larger than if a circle would be drawn around the points of impact, but the results will at least be comparable.
Sten #1 gives an R100 of 17.8 cm when firing single shots. This is around the same as the PPSh and Suomi submachineguns, around the middle of the pack. The mean point of impact is off by 28 cm to the right and 10 cm down. This is quite bad indeed, among the worst of the results.
In bursts, the radius is 21.1 cm, which is quite good. Only the Neuhausen performs better. The mean point of impact is off by 6.35 cm right and 21.6 cm down, which is actually really good as well.
Sten #2 is a little less reliable, jamming up every time full auto is attempted (but firing off 6 mags initially without issues). It also has issues with dispersion. R100 in single fire is 22.9 cm, significantly worse than its brother and any of the other submachineguns. The mean point of aiming is off by 2.5 cm to the right and 12.7 cm up, however, which is pretty good.
Firing in bursts, the picture is reversed. Sten #2 has an R100 of 35 cm, around the same as the PPSh and Suomi. The mean point of impact is off by 22.9 cm left and 28 cm down, which is the worst result.
The Stens jump all over the place, doing rather average overall. However, considering that the other guns were produced in peacetime, while the Sten was a wartime design and produced by relatively inexperienced hands, the end result is actually quite impressive.