I doubt Alfine 8 would work on the cruiser due to hub spacingI have used an Alfine 8 hub. I think they're reasonably well built and nice to use. And unlike the 11 speed version of the Alfine, the Alfine 8 has a gear that is direct drive (1:1). I always suggest setting up the gearing so that the direct drive gear is comfortable for cruising on the flat and gentle hills. That way you get single speed efficiency most of the time, and you only lose energy through the internal gears when you can't ride comfortably using the direct drive gear.
This gear calculator includes an Alfine 8 setting:
https://www.gear-calculator.com/?GR=SHA8&KB=44&RZ=17&UF=2215&TF=90&SL=2.6&UN=KMH&DV=gearInches