Stim
The modulus of the fibre doesnt necessarily have anything to do with strength, it means the fibre reaches its yield point at a lower strain. Yes resin to fibre ratio is important, but if the product is made from several autoclaved sections it probably has a reasonable fibre content. Going from the factory photos ive seen some of these frames are constructed in this way. QC, well thats all speculation, do your own, do a massive drop on your frame and see if it breaks!
Chinese stuff is usually sold in MOQ of 100s, check out alibaba. They probably sell small orders because there so mnuch mark up on bikes in the uk and there is a demand for it. I have bought sample quantities of bike parts from taiwan, the MOQ on most parts was 100.
As for import duty. it depends on how savvy the seller is. If they dont declare the value honestly then none. If they decalre it (and your item is insured forn that) then assume 20% plus £15 for parcelforce handling fee.