I bought the REO's after reading the reviews here after having 3 pairs of cx300's breaking in just over a year and these are what I compare the REO's to, that and my HD280's.
First off their sensitivity is WAY less than the cx-300's (100dB vs.112dB) This is a huge difference and so their max volume is also less and if you are like myself, using them with your phone, this is a deal breaker in itself because walking down a street at peak hour they just arent loud enough, not to mention I am draining my battery faster. Admittedly my nokia n82's amp is under powered but so are a lot of phones.
Moving on to the sound, the REO's definitely respond more to dynamics in music and fidelity is better generally than the cx300's which I liked but the mid to upper range is without a doubt far to emphasized making cranking choruses with singers pushing the point just plain painful to listen too.
The bass?....well there isnt much, I like what my sub does for music bellow a 100hz and the RE0's just dont represent it accurately/enough below around 70hz , especially emphasized against the inflated mids and while the cx300 bass is a little over done and loose at least it has some that u can tame with eq if u wish, increasing bass with eq is not as good a solution for the REO's, I had to push my eq to 80% to get a track of mine I am mixing to a close approximation of what it should sound like with the sub bass melody.
A big part of the reason IEM has taken off is because of the increased bass they are capable of compared to earbuds, I have earbuds with more bass than the REO's.
The high's are nice enough but sibilance is a problem as u move into the mids on some tracks.
Music making and mixing is my life so it is with at least some experience I make these comments, that and I have seen how damaged ears perceive sound in the mid range with the desire for terribly inflated mid/highs that result from it and continue to damage those ears. This is an important point to consider when it comes to IEM's while they inject the sound right into your ear drums.
I am still 'breaking in' the REO's but I cant see this changing much of the above and while the cx300's are nothing special in regards to creating space/detail/dynamics they are still a better solution (while they work) than the REO's and I will now never buy another pair of IEM's under 110dB sensitivity. The RE3's seem like the next thing to try.
the search for a decent pair of IEM's at a sane price continues.