I have just recieved my Armster armrest from RUI, and its just been fitted with the ease as described in earlier posts. As I am only 4'11 I drive with the seat totally forward and for this reason can only benefit from resting my elbow on the Armster, but I think that will be good enough, but the biggest benefit for me will be the additional storage, as I do not have the underseat space.
As I have the black leather sport seats, it looks excellent, as though it was integral to the car.
Overall I am very happy with it, and would recommend RUI, the purchase was easy and prompt and its a very good price.