I would like to buy the item named PiCapture SD1, but first i need to clarify a question.
Could i overlay some text or graphics on video?
The PiCapture video is presented to the Raspberry Pi as if it were coming from the Camera, and so all of the graphics capabilities that can be used with a camera can also be used with PiCapture. This includes overlays.
The approach depends on just what you want to accomplish – you can use picamera to overlay images on the preview window:
You can also use OpenGL on the Raspberry Pi. If you google “raspberry pi camera overlay” you will see some ideas.