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 you recommend to use ubuntu-device-flash 
 but i use to flash with TWRP with great backup functionis it compatible still have TWRP after flash ? 
 and if not how to put ubuntu touch with TWRP ?Regards 
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 yeaaaah google is your friend (sometime) 
 somethings i will read before...
 How to Flash Ubuntu Touch on OPO using TWRPhttps://forums.oneplus.net/threads/how-to-flash-ubuntu-touch-on-opo-using-twrp.431640/ 
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 so this tutorial use image from twrp backup ... :o(