I don't think much of clavenetjunkie's reviewing style - and the comparison demo is meaningless. You can't learn anything about a headphone by listening to a recording of it, through some other headphone connected to your computer. If you really want to know what a unit sounds like you have to stick it in your ears. No other way. However, his measurements indicate a spike in the presence region (he puts it around 5k) which does correspond to my subjective impression. Haven't seen any other graphs for the U1, but I will be curious to see if that is confirmed in other measurements. If measurements show it is there, that is presumably a deliberate tuning choice by the manufacturer - but a risky one. It can enhance vocal clarity and detail, but human hearing is super-sensitive in this range and it's easy to overcook it. Of course whether this is a flaw or a feature depends on your sonic preferences. Have to experiment with EQ to see whether it can be toned back a little.
From my experience with lots of currently sold IEMs - most of them having elevated upper mids to bring more emotional and engaging sound. Some have more evident effect and some are not. It seems that I am not very sensitive cause I don't want to change anything in the sound of U1. But I would for some other IEMs... I've tried to take a graph but my mic is having more influence than it should - most of the IEMs show the same graph with it. So, I have to think of buying some special microphone with specified FR to subtract it from the IEMs grap.