i was tips searching for the Mifo o5... the o5 standard has a weird case concerning vacuum inside the ears: it sounded clear and open when i pressed it slightly and break the vacuum, but as soon as i let go it will suck the air inside the ears (like plunger effect) and cause the mids to sound choked.. that could make the o5 sounded veiled.
so with the o5 it is better to use eartips that a bit hard, or can "breathe" a little
the best tips i found so far is foam tips (i think any foam tips are fine) and ortofons, but because of the case design, i ended up having to put on/off the eartips everytime i use it. better sounding, but slightly inconvenient
so i use this eartips i found on AE, so far working nicely.