Agreed. I have read the documentation:
https://documentation.meraki.com/General_Administration/Firmware_Upgrades/Managing_Firmware_Upgrades
https://documentation.meraki.com/General_Administration/Firmware_Upgrades/Cisco_Meraki_Firmware_FAQ
https://documentation.meraki.com/General_Administration/Firmware_Upgrades/Meraki_Firmware_Release_Pr...
From what I read, if one upgraded to the most recent stable release candidate, then a new stable (or potentially not-classified-as stable) release candidate being released will only be support with "best effort". Quoth the Release Process documentation: "The latest stable release candidate firmware is fully supported by our Support and Engineering teams. Older stable release candidates are supported with best effort; an upgrade to the latest beta, stable release candidate, or stable will ensure full support. "
To me this suggests that one should absolutely stay away from all release candidates, even if they are labelled as stable, unless (1) there is a very specific known security fix, (2) a device is experiencing a major issue that Meraki support says will be fixed by a specific release candidate, or (3) an organization has enough extra Meraki gear, time and interest in testing release candidates. But to partially address item #1, the documentation says that "Critical updates, such as those to address high-impact security vulnerabilities, may be scheduled on a shorter timeline."
Quoting again from the Release Candidate documentation on the "Stable Release Candidate" section: "These upgrades can be canceled, modified, or reverted using the firmware upgrade tool on dashboard." That seems scary to me, but maybe reverting is easy if one just opens a support case.
I'm happy to be wrong, corrected or exposed to other opinions on the utility/scariness of pushing the Stable Release Candidate to any production (or soon-to-be-production) device.