I used Light Flow on my Samsung GS3, my G2 D803 on 4.2.2* and on 4.4.2. Everything is working perfectly (native and 3rd party apps).
*That said, I initially had trouble when I first got my G2, Light Flow would not work, and the LED only blinked on native apps. I tried everything I could think of, including contacting the developer of Light Flow, who was very helpful but we could not resolve the issue.
Finally, I did a factory reset but prior to that, I turned off backup/restore of data to Google servers, and also turned off the auto-updating of apps in the Play Store. After the reset, Light Flow started working and has worked ever since including after update to KitKat.
It is my theory that a setting from my GS3 was restored onto my G2 automatically when I changed devices (i.e. shortly after signing in to my gmail account when I got my G2). Some setting I think somehow interfered with Light Flow working. While it's possible that the factory reset itself fixed the problem, I still think it was the data restore that caused my issue. In any event, that data was just a few preferences, wifi access point, bluetooth pairings and such, no big deal to set up again (you do NOT lose email, contacts, calendar, etc. -- that is entirely different from what I mean about backup/restore of data on Google Servers).
Klotar -- Supervising Manager,
The Department of Redundancy Department
LG Optimus G2 D-803 | Android 4.4.2 | Rogers Wireless