I am considering upgrading from a C7 to a C8 hub and would like to confirm the differences.
It looks like the major change is the Z-Wave 800 series radio and the antenna. So I am hoping that it is backward compatible with the 700 series devices and given the external antenna's it should have a greater range even on the 700 series devices.
I used a C-7 for 3 years and recently upgraded to a C-8. All of my Zigbee and Z-Wave devices worked perfectly after migration. More than that, all of my Zigbee devices talk directly to the hub now. And about 90% of the Z-Wave ones do too. The external antennas and 800 series radio really rock. And the new Zigbee radio is stellar.
Zwave is generally upwards and backwards compatible with all other zwave devices. An 800 series hub will work fine with all Zwave devices back to 100 series.
The external antennas work great to increase signal range and reliability over the internal antennas of the C7.
The Zigbee difference (1.2 in C7, 3.0 in C8) seems to be a larger transition for a lot of folks on the forum. Some have had zero issues with migration. Some have had problems with devices falling off or other problems. Personally I've seen no Zigbee issues myself, but all my devices were 3.0 anyway.
I got a C8 and pretty happy, one of my V1 devices soon dropped and have not been able to get it back cause the new chip does not like the V1 chips, and same with my Ikea blinds. I have my old C5 doing work for devices that cant connect to it, not entirely happy with that part (the V1 sensors are cheep, but by Ikea blinds are pricy)