The main difference between the Braun Silk-épil 9 Flex 9004 and the 9001 model lies in the additional functions and attachments that come with each model.

### Braun Silk-épil 9 Flex 9004
- Comes with a variety of attachments, including an epilator head, a shaving attachment, a trimmer cap, an exfoliation brush and a massage head.
- Has a 360° flexible epilator head that can adapt to body contours.
- Often includes the SkinSpa set, which includes additional brush heads for the face and body.

### Braun Silk-épil 9 Flex 9001
- Is often the basic version of the model and comes with fewer attachments compared to the 9004.
- Includes the epilator head and possibly basic attachments such as the shaving attachment and exfoliation brush, but not the extensive SkinSpa attachments.
- Also has the 360° flexible epilator head, but fewer additional functions and attachments.

Overall, the 9004 model offers more variety and functionality through the additional attachments, while the 9001 model offers a basic yet effective epilator experience.