The Sonos Sub-Mini offers great bass/low-end response at a substantial cost savings versus the Sub (Gen3). In a small to medium size room it’s more than adequate in most environments. 

I have a Sub-mini in a bedroom and in my garage bonded to Era 100’s in stereo pair. Although the garage exceeds (IMO) the definition of a medium size room the topology is concrete floor, smooth walls and ceiling with no plush accouterments. In both spaces the Sub-Mini sits in a corner using the floor and two walls to boost bass response.

As with any sub...placement is a key factor to accentuate the bass response. Other than bigger bass (which is a given) another reason to opt for the Sub (Gen3) over the Sub-mini is placement options. The Sub-Mini (because of its shape) doesn’t offer the placement versatility of the Sub-G3; such as unobtrusively behind a cabinet or under a sofa. 

Just food for thought when considering which Sonos sub to purchase where cost is not the deciding factor.