I am trying a T5p right now (still burning it in...), but am on the fence and probably will return them. I don't have a separate headphone amp and was hoping it would work well straight from an iPhone, and in a sense it does. The airiness, clarity and separation are wonderful, but, at least un-amped from my iPhone, it is too bass-shy for my tastes. It gets better when plugged into my laptop, which I assume has a stronger headphone circuit. Indeed, a lot of tracks sound really wonderful out of my laptop. But, to echo another post on these headphones from somewhere on this site, although the bass is fine at louder volumes, it gets lost at lower volumes. To be clear, I'm not a bass-head and picked these up because my current headphones (Sennheiser Momentum) are too bass-emphasized on some tracks.
The best comparison I can make is to the Etymotic ER-4 (and its variants), which has incredibly clarity, which I loved. Unfortunately, they were too bass-shy to keep, and I eventually ended up with a Westone ES5 (unbelievable mids/clarity, very nice bass, and recessed treble...I guess you can't have everything). The T5p has mids that remind me of my ES5, but with much nicer separation and sense of space, but with a sound that is recessed at the other end of the spectrum.
I certainly could pick up a nice portable amp (I'm considering ALO's National), but the tradeoff (compared to the Momentums) in complexity, cost and comfort (they are only "OK" with glasses) probably is not going to be worth it for me. Even though I got a great deal on the T5Ps, for that kind of money, you really expect a set of headphones that are close to perfect for their application, and here I don't really believe that these are truly "portable" headphones for several reasons, sound included. Hopefully, one of the top manufacturers will continue the trend of high-quality headphones at the $250-$400 level geared towards iPhones and the like, but with a sound signature that is more neutral, prioritizing clarity over bass.
To be clear, there is no question to me that the T5ps have much better sound quality than the Momentums, even with the recessed bass. But the Momentums are quite nice (great, even) in their own right for their target use, and the cons to the T5p make it a much closer call than I had been expecting. We'll see...