It’s mostly about tracking distance.
DepthSense 311 (DS311) has close and far range tracking but it is bigger than the 325 and also has less depth resolution.
DepthSense 325 (DS325) has been designed as something you use with a PC and it focuses only on close range tracking distance.
Typical uses for DS311 are living room experiences, healthcare and recovery games, indoor advertising campaigns, full body tracking for art installations, and academic research.
Common uses for DS325 are PC games, scanning and 3D printing, robotics, hygienic environments such as public spaces or operating rooms and dentist cabinets, and vending machines.