I (perhaps erroneously) regarded the SunTour U (and the very similar SunTour Hero) as being versions of the SunTour Honor manufactured down to a price, and fitted as original equipment on Japanese made bicycles.
Having said that, this SunTour U seems to me to differ from my fourth style of Honor only in that it has a hex head hanger bolt instead of an Allen key version and is missing the plastic spring cover. Surely these changes can only have saved some tiny fraction of one penny in the overall manufacturing cost of the derailleur. Still, as they say in Aberdeen, if you look after the pennies the pounds will look after themselves. Personally I have never found this saying to be even remotely true - my credit card bill obstinately refuses penny therapy - but there we are.