I had a similar issue and I needed a real-time syslog monitor to see the traffic (inbound and outbound) passing through our MX100 Firewalls. I found Syslog Watcher as an option. You can get a 30-day free trial and if needed, support can extend it...and extend it...and extend....I digress.
We ended up purchasing it because it is a pretty powerful real time monitoring tool and it only cost $250 for a year or $450 for 3 years.
It has helped tremendously with real-time traffic viewing from the firewall. If anyone questions whether or not data is getting to, through, or blocked by the firewall, this software can let you know and answer right away. Filtering is pretty simple, show you by-the-second traffic, and you can store logs to go back and query previous logs.
It would be nice if the real-time feature like the Cisco ASAs have would be available on Meraki. This wish has been on my list for a while.
CMNO, CCNA R+S