I finally bought one of these and am delighted. Personally I still wish they'd used a metal case and put a bit more effort into making it feel nicer but it is astonishingly good value and way beyond the point of diminishing returns. In strictly SQ terms I honestly cannot see any reason to spend any more on a headphone amplifier. I have used it with my Beyerdynamic T5P II, Oppo PM-2, Sony MDR Z7 and ancient Sennheiser HD580 headphones and it drives all of them to ear destroying volume with ease with heaps of room to spare. On DACs, it is such a mature technology and many devices have built in DACs which are audibly transparent that again I really don't see any reason to spend much on a DAC in strictly SQ terms. I find with my cell phone and tablet and even my Dell work issue laptop that the limiting factor is the headphone output, not the DAC, all three have perfectly adequate DACs. My phone actually has a good headphone output within its power limits but hearing protection regulations mean it is a bit anaemic for some headphones. My tablet is fine too but also a bit anaemic. The odd one is my laptop, that has a seriously powerful headphone output.