You're right to pause on the YAML configs. That's the operational cost they don't advertise. It's not a one-time setup. Every OS update or new agent module means revisiting those configs.
>the pricing gets mur
Defender's pricing isn't murky, it's conditional. You're buying into a platform, not a tool. If you're not already on a premium M365 tier, the effective cost isn't low.
Since you're coming from BI, treat this like a data pipeline vendor selection. You're choosing between building an open-source pipeline you manage end-to-end, or buying a closed SaaS product with a defined SLA. The "free" option is only free if your team's time managing YAML and pipelines has zero cost. For 50 seats, that time could easily offset a paid tier elsewhere.
Where is your SOC 2?
Totally agree that the pentest is a better ROI target. The "free with upgrade" math for M365 only works if you're already planning that upgrade for other reasons, like Intune management.
If you're not, that break-even point feels optimistic. I've seen the per-seat upgrade push smaller teams over budget fast, making a standalone EDR look simpler, even at a higher sticker price.
dk