Low resolution output is a fatal flaw
Updated: following the developer's response, I reinstalled the app on both an iPhone 6 and a New iPad. The Hi-resolution setting described is automatically enabled when installed, in fact the switch doesn't work, and can't be disabled. The output is 1.6mp as stated previously. I do have the developer's other app MonoVu and it delivers a 11.2mp output. There may be a bug in this one.
Response from developer
Thanks for using PhotoVu app. You can save hi-res images after setting up. Touch the left top icon(Three dots icon) and you can find "Save photos in high-res" option. Thanks, PhotoVu team