I always loved the dual rear sprocket setup used on my '68 Harley Baha 125.
I forget what the ratio change was, but the sprockets interlocked, and 4 bolts held them spaced apart, or rotated 45° and dropped the large sprocket over the small. The rear wheel didn't need to be removed, and just a short length of chain was added / removed. There wher 4 bossed which dropped in holes or worked as stand-offs, along with the 4 bolts.
When I bought my '05 TW, the guy I got it from had changed to a 47t rear (I thought he told me it was 45), for road riding. I've not been happy with 1st gear off-road, and I have some trouble keeping 55 on big hills (I'm 240#). I changed back to 50t tonight. The TW had 850 miles on it when I bought it, about 1900 now
I am not looking forward to it screaming it's guts out, so I'll keep the speed down to 550-55 on the road, which is where it feels more comfortable anyway. I'm talking about handling, not vibration.
Hopefully I'll be happy! I really wish they put a 6th gear in...