I used to run an acessport when I had my mazda mps they are a really good peice of kit to use for mapping. Has he bought it second hand or brand new because if it was second hand and still paired to a car it's not cheap to get it unpaired maybe £70 or so hence why they go relatively cheap if they still are. It takes nothing to install it just in the obd port then follow the steps on the screen theres a thing where you turn the ignition off and on at some point.
Is he using it for mapping aswell not aware of any tuners using them over here for the imprezas, still they are really good giving data on the car a bit like the toucan displays people have.