I have a nichols aluminum flywheel in my M695. I think it's a little over a year old at this point with about 6k miles on it. No problems at all. I would not go back to the stock flywheel, but as mentioned the nichols requires a finer touch on the throttle and the engine braking feel is a bit different. There might be some more vibes, but nothing irritating or mirror-blurring. I have no issue with around town riding. I had it out recently to do some shift linkage work and the flywheel splines looked absolutely perfect. Just a datapoint...
BK
+!
I too have the Nichol's on my M900.
No issues in traffic at all.