I also have the MiNT InstantKon RF70. Have not yet used it much but today I shot 4 packs. Indoor (museum) without flash I found the exposures reasonable right. Outdoors, it was very sunny with blue sky, hard light, too much contrast in some cases. Used the camera in aperture priority (f 22). I found my camera to give wrong indications if the red led appeared. When the window showed "4" my picture was underexposed when using ND4. If I used the ND2 filter instead the exposure was good. Same when "2" appeared. If I used the ND2 it was underexposed, without ND filter exposure was good. Arrived at home I took two pictures, one after using a light meter and one in aperture priority (both at f22). There was not much difference between the two pictures. Think there are sample variations that need to be corrected in production I also would like that the frame lines in the viewfinder must be better visible.
Perhaps half f- setting could improve usability.