They can be written to in spindle-based or tray-loading CD-R / CD-RW burners (and read in spindle-based or tray-loading Compact Disc players) but there were also some devices that were specifically designed around the Mini CD-R/CD-RW.
One of these was a number of models in the Sony Mavica line of digital cameras. The first of these was the MVC-CD1000 released in 2000, which could record to Mini CD-Rs. Later models in the line (the last of which was released in 2003) could use either Mini CD-R or Mini CD-RW.
There was also a portable Mini CD-R burner called the Imation RipGo! that was introduced in 2001. This could burn MP3 files to disc, and also play them back. Sony also introduced a Mini CD burner (called the PhotoVault), allowing pictures to be saved from a Memory Stick, USB flash drive, or camera with a USB connection.