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They are both Nittaku poly balls, are both white and round, but have different playing characteristics to each other, are made using different techniques and in different factories. Not in the least confusing, eh?
Nittaku SHA is a DHS clone made in China and plays like all the other DHS/DF clones.
Nittaku Premium is made in Japan in Nittaku's own factory. It's a seamed ball, but the seam is very thin compared to DHS/DF. The Nittaku Premium ball reportedly plays better (closer to celluloid) than DHS/DF or XSF, but it's fragile and expensive.
If it says seamed, expect it to be similar to dhs or double fish plastic balls. However if it says seamed and made in Japan or Germany, expect it to be similar to nittaku premium 40+ or butterfly G40+. And if it says seamless, expect it to be similar to Xushaofa 40+.I have ordered some plastic XIOM balls since that's the only xushaofa I can find in Greece. Did look at tt11.com website just to double check the price and saw another new ball appearing in the front page, XIOM Pro Select 40+*** (seam plastic ball). Price is the same as the XIOM Seamless Plastic Ball. Is the new ball like DHS and all those bad quality, easy breaking balls?