Having used Bulgarian, Polish and certain US polymer magazines, I am a convert. Steel is just too heavy for the same result. AK is a 3-4MOA rifle and yet nobody questions the utility of a red dot sight for improved speed and precision.
While the RPK-derived Vepr 12 are unlikely to be more accurate that the rifles, they are not appreciable less accurate out to the transonic range of the slug in use, especially if the slug is of a Brenneke type. 4MOA out to 60-80 yards isn’t unusual, and rifled shotguns can approach 1.5MOA with Brenneke or sabot slugs. Here’s a PDF illustrating terminal performance of slugs at long range, and a video showing slug use at 230 yards. So better sights are a plus even for smoothbores.