happy new year, and welkom to the Fairphone form.
i understand you are thinking about buying a Fairphone, and like to know the experience of user’s how already have, i think you on the right place 
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about the network coverage in Hongkong:
maybe ther is a wiki already available, listing where the Fairphone is already used and experience of the users on different network operators?. its a common question.
i can’t find the wiki now.
sorry i have no experience with a FP5 in Hongkong,
well Fairphone don’t garantie the coverage outside of Europe. i never had any isu traveling, using a non EU simcard and haven’t heard anyone before about a country where the phone is not working on the mobile network.
About the camera
i can tell a little about my experience with it, well i think its very depending on wat you need like or prefer.
yes the camera software not excellent, but its definitely not bad. you can make very good pictures with the camera. and is possible to install different software as well if you like that. i never tried. using the stok app, i don’t have much complain about that. and Fairphone is still improving the software so it will become even better over time.
only in low light and fast moving things, it gets difficult to get a great shot.
all together i will say the camera is working very well, i like it.
same time that is just my experience and opinion.
may a few helpful links: