i wont trust tianya nd quality. i got one bad nd8. i can literally see particles in it actually. realised it is affecting my pics badly when i'm using now. considering to get a b+w 10 stop maybe, rather than stacking an nd4+nd8 which is quite bad.
tianya isnt quite stable. but my gnd is fine. the color grads are fine too. cpl seems not as effective. or maybe i'm not good at it yet. but the nds are giving me headaches.