For anyone else who is thinking of adding this bar to their base Impreza: DO IT!
The install was quite straightforward. The improvement is very significant.Going from no rear sway to a 19mm, the body roll in corners is greatly reduced. I am more confident in corners and it is generally more pleasant to drive the car in the city and just more driveable in generally. It also feels less susceptible to cross winds on the highway. My significant other was so impressed that I am going to put a rear sway on her Honda which is also a base model and doesn't come with one!