The ST & the HD appear to mostly share a chassis, but that's about it.
The HD, which is no longer available in the U.S. either, also has an external fuel filler, something I appreciate.
The motor in the ST looks, by spec, to be the same one used in the Lance scooters in the U.S.
Not a terrible motor but notably less power than the HD, & a bit less than the People S, also not available in the U.S.