Looks-wise, I personally don't think it adds much. BUT I have seen women get into the vehicle by using them and don't contest that it could serve real use if the driver is on the shorter side.
I test drove a few X5s with it and it got in my way so much that I would have no part of it regardless of cost... $300-something is pretty cheap anyway in the big picture. In hindsight, I may have gotten it for my wife to use on the passenger side because the sport seats make it harder for her to get out without pushing the sides of the seats down (which is not ideal)... and I would just deal with it. I would say it depends on your situation, but I'm voting no.
One thing I should mention while we're on this topic... my wife claimed she saw a vehicle with motorized boards/steps - they come out when the door is open. They fold back under when doors close... she thought it was a Lincoln or something... anyone seen these?