This is my first tube anything, so I don't really know what to expect. Before getting into the sound, beware of the build quality. The unit I ordered first showed up with a slightly messed up socket that caused the tube pins to bend. I tried bending them back in place, but ultimately couldn't get them lined up properly and the tube shattered and cut my hand. The replacement showed up showed up fine and I was able to install the tubes easily
Out of the box, the unit with the included tubes sounds ok. Not a huge difference from my TT's built in pre. They're oddly bassy and a bit hollow sounding. The real winner is this unit combined with the recommended replacement tubes. The bass tightens up while still retaining a solid punch. Around 12o'clock is the sweet spot for me. Maybe around 1o'clock on the treble knob adds a nice extra sparkle. But again, this is with the replacement tubes. The included tubes don't EQ as well. This is going directly into a set of Edifier active speakers with the EQ set at 0
The headphone jack is a huge disappointment, especially considering that's almost the sole reason I bought this. I tried on a pair of Sennheiser HD 599's and Audio-Technica M40x's. The full sound coming out of my speakers was completely gone and no amount of EQ brought it back. The treble seems to come through, but not the bass. Even with the volume turned down low for listening on headphones, I could hear and feel the bass coming out of my speakers if I dimed the bass knob without hearing any change on the headphones
I'd say this is about a 3.5/5 because of how cheap and upgradable the unit itself is, provided you get one that passes quality control and doesn't have a bad socket. The included tubes are forgettable and hard to justify using when a better set is only around 25 bucks. The onboard EQ is nice and can make some tubes shine more than others. Worth getting with replacement tubes for just starting out