Do you remember Teddy Ruxpin? It was a toy bear that was popular in the mid-80s. You popped in a cassette tape and the bear sort of came to life, sang songs, and told stories. I'd say that Tonies are more similar to a Teddy Ruxpin than an Amazon Echo. Much like Teddy Ruxpin, the Toniebox needs characters to bring it to life. You pop the character on top of the box, and you'll hear stories and songs that are unique to that character's world. You can't use it like you would a radio or an IoT device; it's actually quite limited.
I assume that the sound quality is enough to please a child. Your young niece isn't likely to pick it apart for having too much reverb. She'll simply be delighted that Princess Jasmine is singing to her.