I traded in my 2010 FLHTC on the 2013 FLHTCUSE8, and my first impression is that it the SEU get's a little squirrelly when following larger vehicles. I notoriously ride closer to the cars in front of me than I should, so I get quite a bit of turbulence from the vehicles I'm following.
I didn't really notice it on my 2010, but it was really noticeable yesterday (which by the way was my first ride longer than my 1 mile January ride on it after buying it in mid December, 50 miles!) on the SEU. I also had a 17 MPH crosswind, which didn't help any.
When I got closer to pickup trucks with toppers, I could feel the buffeting and it felt like the entire front end was loose. As I backed off, the buffeting was reduced and it felt better (still had the crosswind to deal with).
The differences between the two bikes is something else that I may look at.
1. Windshield height. I had the tall windshield on the 2010. Could have something to do with the way the air hits the new shorter one that causes the buffeting to feel more severe. I'd expect the windshield with more surface area to exhibit that behavior, but it didn't. I have a short Klock Werks windshield that I can put on, but I'll wait for the temps to get above 40.
2. Super Reach Seat. I replaced the stock heated hammock seat with a "super reach" seat, which moved me forward a couple of inches. It also dropped the seat height another two inches. The change in the Center of Gravity (CG), could also be a factor. I could check that easy enough by having my friend ride as a passenger, which would shift the CG back a bit. This solution is a stretch. I don't expect it to be the problem, but I am thinking out loud.
3. Weight. The weight of the SEU is about 100 - 150 pounds heavier than the 2010. I ride with a passenger quite often and don't consider the weight gain to affect it too much. However it depends on where that extra weight is. I could do a quick check by putting it on a floor jack and compare it's "balance" point to where the 2010 was.
Right off hand, those are the thoughts I'm coming up with. I need to mention that because I am vertically challenged, I had the dealer lower the front forks and the rear shocks before delivery. It could also be that the shortened springs up front have changed the handling (that's going to be a bit harder to check without the original springs).
My overall impression of the scoot so far is that it is a pretty good step up from the standard Ultra. The extra power is exactly what the Ultra needed. The creature comforts are nice, and I'll be able to comment on those when I get the chance to take a real road trip. I am very happy with the bike, and look forward to getting some more road time under my butt in the near future!
These are just my "out loud" thoughts on my impressions and opinions. We all know that opinions are like butt holes, "Everyone has one and yours is the only one that doesn't stink..."
Cheers!