This review is coming from a METAL guitar player. Rock, country, pop, blues players will likely NOT love this. So here goes...OK - blown away by the distortion honestly. Been playing thrash, speed, death, black metal for 20+ years as a hobby and stress release. I'm a tone and distortion s*ut and can spend hours tweaking stuff on my racks to get it right. Cheaper pedals, headphone amps, and mini amps NEVER have enough distortion and oomph for me. I rarely get enough distortion and "kick" unless I putz with a 20 band EQ all day and use whatever the heaviest distortion is available. I don't do "crunchy". I do "melt my face off!". "Everything at 11 !" - is usually still not enough.But this little gem has MORE distortion than I need. I've NEVER said or written this sentence in my life before. Ever.Right out of the box I plugged it into one of my Ibanez RX series guitars, plugged in an AKG set of cans, dialed everything up and BOOM - Dimebag Darrell (RIP), Chuck Schuldiner, or Slayer sounds - like, OMG!I had to dial the distortion DOWN about 20% to clean up the tone a tad.Again, never thought I'd dial down distortion on anything lol.The little Tone dial does wonders, too. All the way up it's a crazy treble-heavy death saw from hell that's just fricking awesome! Small incremental moves of the dial change the tone quite dramatically so be careful with those sausage fingers!I'd say the tone range is somewhere like a Solano amp, all levels up, mic'd up cab on side axis. Maybe also some Marshall with dual V-Type Celestial cones, depending on your tone and drive settings. Of course your ears, guitars, and headphones all will make a difference too. YMMV.There's a dial for volume (SUPER loud, depending on headphones), Tone, Drive (that's Distortion), and...that's it! All you need, honestly. These dials will get you from filthy clean-ish to DEATH METAL skull drills.There's a simple On/Off switch (thank GOD this unit doesn't do the one-button-does-it-all BS like some others)There's a "FX" switch on the side and it just adds a delay effect with some extra reverb. It's alright for practice but certainly not the main attraction here.Haven't tried the line input so I can't comment on that.As for build quality - it's not great. It's thin plastic and I'm worried something's going to fly off at any moment, especially the on/off switch or the dials. In fact, I broke one unit when I accidentally sat down with it plugged into my guitar. The unit got squeezed on the bed, and the headphone jack broke (!) the unit's internal headphone input and it vanished somewhere inside.Usually when something is built as badly as that, I throw it out or return it. In this case, the sound is so fricking sweet, I immediately bought another one. And a different one (Mini Turbo, pictured) to try that one out too.I haven't heard of Donner before but somehow they manage to make incredible digital sounds in those tiny boxes. I'm gonna buy 'em all. If they do the other sounds as well as they do METAL, and for a little over twenty bucks, it's worth it. Will leave a separate review for the more expensive Mini Turbo.Besides the rather flimsy hardware quality, my only other gripe is that it charges with a MINI-USB. Not micro. MINI. That's the one where you probably don't have a cable lying around for anymore because it's an old standard. Luckily, Donner provides a (super short) Mini-USB cable to charge the unit. I really wish they'd gone with at least a micro-USB (which they did on the Mini Turbo) or better yet USB-C.Personally, I would be happy to spend twice the amount IF they increased the housing /hardware quality, and added USB-C or at least micro USB charging option. The sound is THAT good (again, if you're really into hard metal).To be fair, I realize they can't make the housing TOO heavy because then it'll unplug itself from the guitar. (All the weight is on the plug and you REALLY don't want to sit down with this one, see above)Not recommended for Country, soft rock, pop rock. This really is a METAL headphone amp.Hope this helps my fellow Metal brothers and sisters!