I was debating between this and the regular echo. I've had both and we both know what the echo does so all I'll talk about is the sound quality.
I'm going to get to the chase. This is the BEST speaker I've ever heard for under $50. The functions of the echo along with the music playing functionality and the sound quality makes it a steal at this price point.
The sound is great for its size. It can get pretty loud but the bass is definitely lacking. The bass isn't god awful but it just isn't there.
Now I will say this... if your primary motivation for a speaker is to listen to music, go with the echo. If it is but your budget is under $50 then go with the dot. It won't blow anyone away during a get together in your living room but it'll get the job done. The dot will only flourish is an enclosed space. It needs walls nearby to bounce off to cover up the weakness of the bass.
If I had to compare the sound to another speaker, I'd say the UE Wonderboom or the older Beats Pill, all of which suffer from weak bass. For the size, I was impressed by the sound but with the Echo at its refurbished price of $69 I'll have to aim towards that direction.
I'd recommend this for someone who needs an echo for their kitchen, bedroom or bathroom. It's just not going to hold down a living room unfortunately but overall, I like the sound and if I need a second echo, I'll definitely get a dot.