The Shanghai GP3 film is OK, but has faults. It's /very/ curly for one thing : it's /impossible/ to get it flat, even after weeks under a press. The emulsion can have small defects, and it seems very prone to scratches (the fact the film curls on itself doesn't help !)
Beside that. you get fine grain, good sharpness and very good tones. I have a few rolls left, but I won't commit them to "serious" photos, they'll be pinhole or test rolls only. It's just too much trouble handling just a 3 * 6x6 strip by itself !
The 4x5 shanghai on the other hand is fantastic. Very solid, excellent sharpness & tones and the emulsion is nice and smooth. The base is quite thick and you can really manipulate the negs without fear of scratches.
Both film share a thick anti-halation layer, so a pre-wash is more or less mandatory if you reuse your dev. The pre-wash water is quite colorful afterward! 😀
I have plenty of samples from both GP3 in 120 and Shanghai 4x5 in my Flickr page (see signature)