Like the name says, NB LTE-M is narrow-band version of the LTE-M. NB uses 200 kHz band where as the normal LTE-M consumes 1.4MHz. Both versions can co-exists without interfering each others. The purpose of the narrower band is to reduce end-device power consumption and cost. Intel says it will launch low-cost and low-power chips for IoT market using the new technology. What does that mean in numbers remains to be seen.
|LPWA IoT Connectivity Overview|
Nokia White Paper - LTE-M – Optimizing LTE for the Internet of Things
Technologies listed in the comparison above are all intended for public networks. LoRa is the only one which is available for private network applications also. That means you can set up a LoRa gateway of your own just like using WiFi. Sigfox is closed and propriterary technology, and use of licensed frequency bands means you got to be an operator to get the license in hand.
The greatest weakness of LoRa technology is the use of unlicensed frequency band. In Europe, the duty-cycle limitation is only 1%. That's regulatory not technology limitation. It does not affect much the downlink or uplink of many IoT applications, but over-the-air firmware updates are very difficult, next to impossible. It would take awfully long time to transfer any reasonable sized firmware. Perhaps some clever delta (diff) technology for patching the device firmware image could work.
The above comparison is missing energy consumption. It seems to be difficult to find comparable numbers for real energy (J) consumption per delivered payload with different technologies. Mobile data suffers from significant overhead in terms of channel opening, handshaking, etc. Most of the energy is consumed by other functions than transmitting/receiving the actual payload data. As an opposite, LoRa introduces very low overhead. Any technology can provide battery life of over 10 years, it's only question of how much batteries you need.
LoRa is available as of Today. For LTE-M, first device and network manufacturers must introduce new products, then operators must upgrade their base stations. I don't believe LTE-M is really in place next year. Once it's there, the deployment of the technology will be fast for sure.
No convergence of IoT connectivity technologies is visible within the foreseeable future. There are different use cases for different types of radios. Main categories are short range radios (Bluetooth, Wifi, etc), Low Power Wide Area (LoRa, UNB), and cellular data. They have all different nature and no single technology will rule them all.