My only concern here is that calling php module every minute will prevent hard drives from hibernating (which is not only power saving option but will greatly affect HDD life span). Is there an option to query watcher.php from a timer script in main.php? This way the watcher will be invoked only when the application is in use.
I’ll check tonight whether Synology goes into HDD hibernation with your modules executed by cron. If not, it will be an issue.