Hi there, first post from me. Been watching this thread with interest to see if the NX1 was actually any good but as it was so cheap (£21 on ebay) i decided to take the plunge!
Firstly I certainly would not consider myself an audiophile at all, just a major tech head with an addiction to gadgets, so please forgive my unprofessional views.
I bought the Topping NX1 to use with my AKG K545's and iphone 5. Without the amp the AKG's sound great with good instrument separation and a nice neutral bass, with the NX1 hooked up i found that you get a slightly increased bass with much more punch to the the sound, on the flip side i feel as tho the sound is a little more 'merged' with a very slight loss of the separation. The Topping has two gain settings, high and low. High is the setting i use as i found low to be very flat and unpleasing. Overall in terms of sound quality, it does certainly add a little more punch and bass but a slight degradation in terms of the instrument separation.
Build quality is very good with the body being encased in sturdy metal, all switches do their job adequately even if they are slightly small and fiddly with the volume knob being satisfyingly smooth and gives a nice 'analogue' feel. Included in the packaging is the obligatory rubber bands, 3.5mm connection lead, micro usb charging cable and velco sticky pads.
Battery life has so far exceeded all expectations, fully charged the unit on receipt about 2 weeks ago and have mot had need to charge it so far despite daily use of between 1-4 hours a day!!
Overall for how cheap the Topping is i really can not complain at all, might not be to everyones taste but i like it!