What is the MFF2 form factor?

Embedded SIM cards are generally the most common choice for M2M applications because they are vacuum sealed and can be soldered directly to the device card. This increases reliability in terms of reducing malfunction due to shock, corrosion and other environmental factors. In addition, the life cycle of an embedded SIM is typically 10 years, longer than that of a standard form factor; this means that you will generally not need to replace the SIM during the life cycle of your device.
In addition, GSMA's embedded SIM card specifications provide a standard mechanism for remote provisioning and management of M2M connections. This allows over-the-air provisioning of the SIM card, which means that you can remotely provision the SIM card to connect to an initial operator and then change the subscription from one operator to another. Typically, with the 2FF - 4FF form factors, SIM cards are locked to the connectivity provider from which they originated, which means that to change providers you need to physically replace all SIM cards. The ability to provision the embedded OTA SIM card is vital for M2M distributions for two main reasons, i.e., cost: buying all new SIM cards for each of your devices is inconvenient and expensive; access: physical access to all your devices to change SIM cards can be virtually impossible in many cases of M2M distribution due to the global spread of resources, sometimes in very remote locations. Another important advantage of embedded SIM cards is their physical security. Soldering a SIM card directly onto the device's circuit board makes it impossible for anyone to tamper with the device to remove the SIM card to misuse it.