Happy to hear you liked them. Agree on your points, there's no linear justification of iO-12 to be absolutely better than M4s if one enjoys the latter. I do keep both - well, actually more
- because 1) I like different sound signatures so all my collection is on regular rotation, 2) my music preference isn't too hi-fi demanding, 3) I use M4s for commute/work (better mic, better portability, better battery, they're relatively cheap so I don't worry about rough usage), 4) I got some spare budget so no regrets.