Quick impressions of the R4. Got mine last week and so far really enjoying it. This is my first DAP and it's meeting and exceeding my expectations so far.
Sonically, I think the soundstage is pretty good, not mind-blowing. Separation is quite good. Overall, the tonal balance is natural and uncolored. IEMs sound excellent on low gain, and full-sized headphones like the ZMF Bokeh and Hifiman HE1000 V2 sound sufficiently driven on medium gain. High gain, to me, sounds grainy even at lower volumes.
Zero issues with exFat formatted micro-SD card. Battery life is pretty decent, heavy listening sessions with hires files lasted me about 2 days. Playing DSD and FLAC files does get the unit pretty warm, but not to levels that I would consider alarming.
All in all, pretty great little DAP, and looks hella cyberpunk too.