Good question, these custom Firmware binary files update the same as official procedure. Just tested the User Modified v2.6 Firmware against the official July 2018 VIOFO FW v2.6
Modified data bit rate = 30&60fps 28.1Mbps on 3min clip = 616 MB
VIOFO data bit rate = 60fps 20Mbps & 30fps 15Mbps on 3min clip = 400 - 320 MB
There is a slight improvement to Image Quality Sharpness using the Custom Modified v2.6 but not worth doubling of file size. Both v2.6 files produce an over-brightened image, great for night but not day driving, in some clips it blanks out the plates during the day when plate background is white. From the initial release of A119 in 2016 very little Image Control was included in the Menu settings. Other Dashcams now include user settings for Brightness, Sharpness, Color and more. These are built into the current Firmware, but locked and hidden by VIOFO.
Anyone else want more Image Quality Control from their DVR Dash Cam without hacking the Firmware ?