The counter has been 100% reliable so far but we may have just been lucky. A common failure is SDcard/file system corruption due to incomplete writes. To minimize this, it's recommended to reduce or eliminate writing to flash. It's hard to make the file system read-only but it's easy to redirect frequently written files (e.g. log files) to RAM.
The following project makes setting this up even easier: https://github.com/azlux/log2ram
@uwekamper what do you think of this?