If you are looking for a no frills headphone preamp then this is the one for you.
The built-in headphones are the big plus in this product. They provide very good sound quality. Plus, life is so much easier when the headphones are actually part of the amp, and no bluetooth, rechargeable battery or pairing a set of headphones slows you done (compared to the Fender Mustang Mini headphones amp for example, which is nice, but in my view requires too much effort to just plug and play).
As for the sound the amp produces, it's ok. Lower your expectations here, you won't get a tube amp sound from this 100 euros piece. But it does what it should do quite good.
Build quality could be better. The set feels rather cheaply made, simple and cheap plastic. I wish they would spend a bit more here.
Overall, this headphone amp is a very convenience, easy and fast way to play your instrument quietly at home.