HA3D : Such a useful solution!

It is small, uses 2 AA batteries, lasts long, sounds great (if you feed it great sound) and has three outputs for sharing or comparing headphones (reason I bought it).

Know that the pots all have channel imbalances down low, which is normal for cheap ones like these, so you'll need to lower your source's volume to get out of that lower volume range if it's too loud for you.

This thing has a lot of power even with 150 ohm Superlux headphones. I fed it with my Schiit Modius through its balanced inputs. Its sound is better than all my audio interfaces, which are all high-end ones.

I also fed it with the included stereo cable from an H2 Designs MIYO's headphone output. Great sound, much bigger and visual than the already impressive sound from the MIYO. So, this Superlux is decently clean.

The pots and knobs are the cheapest-feeling parts, but overall fit and finish is very nice. I recommend this unit. Sounds nicer than I expected, especially for the price.