Thank you for your response, but I still don't know which product should uses the lib_openthread_master. Ex: Bulb use lib_openthread_ftd, Switch use lib_openthread_mtd.
Basically, the MTD (Minimal Thread Device) library is a limited functionality library. It is suitable for devices that act as end-devices, meaning they will not be routers. So light switches and low power sensors, for instance. There are some features stripped out of this library, such as those required to be a router node, but it also takes up less flash. The FTD (full Thread Device) are router eligible end devices (REED), meaning they can become routers. So this requires a bit more functionality, takes up a bit more flash, but is needed for devices that can act as routers. Typical use cases are mains powered devices, that will extend the range of your network.
The Master library is a full-fledged variant, with all functionality included. This is fairly new, so I guess there were some special features that was implemented, but not typically needed in a normal node. This is mostly used during development, so unless you specifically need a feature that is not present in the FTD or MTD, I would stick to those for production.
However, the features of FTD and MTD only differ in LINK_METRICS_SUBJECT and CSL_RECEIVER , and the size doesn't seem to be significantly different. Why not merge FTD and MTD into one?
It is not only the flash it occupies, but also the RAM it would require to be a router device. It needs to keep track of the routing table, where as an FTD will only ever send messages back and forth between it's parent node.
