I have the OEM, and I actually like it. There are 5 advantages that I can see for the OEM:
1. It can be left on all the time. You can't tell from the pictures, but it is actually curved slightly. As long as you put it in with the curve going the right way (forward), it has a little clearence and doesn't rub anything. We leave ours on almost all of the time.
2. It is bigger, so it is more effective. Blocks more wind.
3. It can be removed in 2 seconds. It has two posts that sit inside two holes that the dealer drills into the area between the headrests. If you don't want it there, just reach back and pull it off. I thought that the holes would be an eyesore when the windscreen is removed, but they aren't. The dealer installs some matching trim around the holes that make it look great.
4. Since the dealer installs it (drills the holes and installs trim around the holes), there is nothing for the owner to do. No screws to unscrew, etc. On a new car, I just don't trust myself to do anything to it.
5. Since it is installed between the two headrests, there is no issue with the plastic causing the trunk to be hard to close. And we don't really know if there are any possible long-term problems to that.
To be honest, there are some disadvantages:
1. It isn't as attractive. No getting around that fact. That is somewhat medigated by the fact that it is so easy to take off, and you can remove it in 2 seconds whenever you want the absolute best look.
2. It is more expensive.
3. It is mesh, not clear. Looking back through the rear-view mirror looks like you are looking through a tinted window.
4. As mentioned, it requires the dealer to drill 2 rather large holes. But with the trim that is added, the holes honestly don't look bad.
When we bought the car, it didn't originally have the windscreen. But my wife really wanted it. So since she was letting me get this cool car, I figured that the least that I could do was have the windscreen installed. But now I'm glad that we did. She has beautiful long hair, and in other convertibles she was hesitant to put the top down. Now we go everywhere with the top down, and she no longer has tangles and knots. A true win-win situation.