I use these for listening to music and podcasts during the day, In other words: Can't comment on on-stage monitoring performance.
Soundwise I can compare to a variety of full-sized headphones. From the usual Suspects, my favorites would be:
Sennheiser HD650, AKGk702, Beyer DT250
All these I consider to be fairly neutral (as opposed to e.g. a Sony MDR V6 / MDR 7506 which is nice, but not neutral).
The Sennheiser IE 100 Pro appear to be mostly neutral to me, too.
Treble is somewhat enhanced as far as I can tell, but not in a dominant way: They are not sibilant and not fatiguing.
So soundwise, I am very pleased. They offer a neutral, great sounding picture.
Soundstage / Instrument separation is very good for a headphone, especially in-ear phones:
The spatial origin of sounds seem to extend well beyon my head.
Replaceable cable is a must. As soon as those disappear, my money will disappear.
My biggest grudge with Sennheiser: Replacement part prices.
There simply is not justification for selling 4 cents worth of plastic foam for 40 bucks. No problem with profit margin but not three orders of magniute. (Looking at you, HD 650 earpads)
Cable for this thing: 40 bucks again. (IE40 cable)
I am looking forward to test durability with these.
Overall: Great product.
