FWIW, if you're looking for a portable headphone amp check out the FiiO A1 @$28 or FiiO E6 @$50 from Amazon. I travel all the time and 1) love the size of the FiiO ... it's less than half the size of this Topping amp and 2) I use the E6 on planes and can attest to its performance.
ddorfs I have both. I'd agree with the E6 recommendation for it's EQ, and not it's measly 150mW (16Ohm) output. Unfortunately, they haven't made it in years and it's replacement, the A1, is deplorable. The S.M.S.L sAp-7 has an almost identical EQ as the E6. Unfortunately, mines a colossal POS (pops, hisses, regularly stops working for no apparent reason).