Hmm..many people opine the same on burn-in, I used to believe the same before this change on MH1C. I put my IEMs to burn-in for like sessions of 20 hours continuous on pink, white noises etc keeping them in a box .. So when I listen to these back, I can notice a change more consistently in smoothing out mids, treble and bass being more deep and punching. I can say burn-in is a placebo for all other IEMs Ive heard till now. However, I can notice the change with A/Bing with my other MH1C.
My friend in Hong Kong has 2 pairs. One with 0 hours (as a backup) and another as his casual one. He has UE11's($1.5K) so I'll leave it to him on what he thinks.
The Dunu DN17 and MP8320 do indeed yes requite burnin. I would say a solid 60 hours for those ones. 300 is just an astronomical number.