Pros: Lush tube amp in a small package
Cons: For some headphones, too warm/lush
I bought this amp on EBay, and got a good deal. It's a nice looking, albeit small, tube headphone amp that uses a pair of 12AT7/ECC81 tubes.
The "Headphone" is very cute, and with some headphones, it was outstanding. But it is a VERY warm sounding tube amp. It's maybe the most tubey, "syrupy" tube amp I have ever heard. With headphones that are already a little warm, like the JVC DX1000, it was a poor match - things were just too warm.
With headphones that could use a little warmth though, like the Beyerdynamic DT770/600, the "Headphone" was great. In fact, that particular pairing was so good I have kept the two together to this day. The 770's need some midrange warmth, and they need a little softness in the highs, and the J Sound Lab provides this. In this context, the overall sound is very engaging and musical.
As a general statement, though, this amp will require VERY careful headphone matching. If you have headphones you would like to warm up, then the "Headphone" might be just the ticket. But if you think your headphones are perfect as they are, or maybe a little lush as they are, then this amp is not a good choice.
Tube rolling can help with matching a little, but even the "coldest" 12AT7's, the Telefunkens, still did not make the J Sound Lab neutral - it was still very warm sounding.
As such, I recommend a lot of caution here. Good results are possible, but only with forethought and care in system design.