Hello Germain38
There are several differences which justify this price difference. You can find more information on our homepage
https://www.irobot.ch
Compared to the next lower priced product, the Roomba i7+, there are the following features:
New 3-stage cleaning system with Powerboost.
- Our most powerful suction (40x vs. Roomba 600 and 4x vs. Roomba i7+)
- Corner brush
- 30% wider rubber brush
- Anti-Allergen System
- PerfectEdge™ Technology
Roomba s9+ can also clean a larger area in less time.
And of course there are several differences compared to the Roomba 900-, e-, 600- series which Pit.hostettler has already explained to a large extent.
Many greetings
Your iRobot Team