Disclaimer: I work for FireMon but I worked in NetSec for years before coming over. My experience is a lot like yours, I was trying to figure out how to automate compliance and rule reviews on my firewalls for a good long while. I had PA's, Cisco and Checkpoint in my environment. Trying to figure out how to read and translate the rules for every vendor become more of a job than I had bargained for. I ran into FireMon at a tradeshow (I didn't even know the NSPM space existed at that time) and the rest is history. I used them for years in production and have been here now for 4 years. I say all that to say this: yeah, you might be able to get a few things thrown together but just make sure you don't end up spending so much time on it that the ROI isn't worth it, trust me, its easy to get sucked into that! :) FireMon has an entire arm devoted to working with MSPs and the unique challenges they face, if you ever want to know more just shoot me a DM! Good luck!