We put a sunnybrook in our 8820 and it was one of the biggest selling features when buying our 9610. It is absolutely worth it in my opinion. You don't get the vibration from dust on the back side of the bars, tough slugs go through much better, when it gets tough you will notice a big difference. The minus is installation they are HEAVY. You don't need the concave and cylinder if you don't want them. I wouldn't run without one. Get the boronized bars as well.
We had the complete set up in a 9610. It really improved the performance in tough conditions. Could probaly run a couple of more hours at night compared to a normal 9600 in the same field. Plus it is nice and quite and no vibration upon start up, and u also can change the bars through the stone trap. We never had to though and we probaly had 15000 acres on the bars.
I don't think it helped the fuel ecomony, but it was hard to tell because we also had a chip in that combine. As far as being harder to startup, our cylinder belt and variable speed belt probaly lasted longer because there was no more slugging when doing wet heavy swaths.
On another note our neighbor has 3 machines with the sunnybrook setup. He had a keyway go on one of the beaters during harvest so he just put the JD one back in. He couldn't believe the difference it made, so after harvest he fixed the sunnybrook back up and put it back in.