Hello,
For my NX1 i was very interested by BlackMagic that seems the best but for a very low budget, i have bought Feelworld FW760 and i am very satisfied and impressed https://www.amazon.com/gp/product/B01H39DDUE
I had an Aputure VS-1 https://www.amazon.com/Aputure-Imaging-Industries-Ltd-VS-1/dp/B00FG709H6/
800 x 480 screen resolution can't beat the full hd of the Feelworld.