There are two varieties of sopranino--the straight model, which looks like a small straight Bb Soprano saxophone, and the curved model (a bit rare), which looks like a toy saxophone.
Both saxes are very playable, and the key structure of both feel like the distance on a Bb Soprano Saxophone.
My mouthpiece is a Vandoren E or F, with Vandoren 2 1/2 Sopranino Reeds.
The two I own are:
Mason (blue and silver) -- straight model
Orsi -- curved model
Both have key ranges from Low Bb to High Eb.
I will put a pic and a sound file here shortly!