Of corse commercial software producers allways have warnings against freeware
That is not what's going on here. Adobe actually recommends free codecs when appropriate. (DNxHD and UT are two examples. Scroll to page bottom.)
http://helpx.adobe.com/premiere-pro/kb/audio-video-glitches-avchd.html
The warning about K-Lite comes from a LOT of users' negative experience using it. Just because you've successfully played Russian Roulette thus far doesn't make it a safe game to play.