What was said earlier about the rollers is that when they are rolled they give a signal just like a button press after each click of being rolled. In other words, it should work just fine.
Also, the RNS-E will not put out a flat signal. Yes, I know that there are people who claim it will and "have" the data to prove it. However, the built in processing of the unit is not defeatable therefore meaning it will never be truly flat.
If your car didn't come with the RNS-E I would upgrade to the 900bt. That is what I will be doing when it comes out.