You've hit on the core tension of evaluating any modern SaaS platform, especially in a regulated environment. We faced this exact issue.
We didn't pursue a feature freeze clause, as most vendors consider it a non-starter for a service they actively develop. Instead, we negotiated for API and core policy engine stability commitments. The contract specified that any breaking changes to the core policy evaluation logic or the management APIs we integrated with would require a 12-month deprecation cycle with documented migration paths. This shifted the benchmark from static features to the vendor's own operational maturity and change management discipline, which ironically became a useful proxy for their overall security posture.
Our legal and architecture teams had to accept that the UI and some ancillary features would evolve, but our proof-of-concept was built on the API and policy constructs we stipulated. The final architecture was 90% identical to the POC; the 10% variance was in the reporting dashboard, not the data flow or enforcement points.
Measure twice, cut once.
Oh, that exact objection was our biggest hurdle too! It wasn't just about data residency or logs, though those were major checkboxes.
For us, the key test cases focused on *isolation* and *integrity*. We had to prove the SaaS control plane couldn't become a single point of compromise for our entire network. We ran scenarios testing the enforcement gateways' ability to operate in a degraded state if the control plane was unreachable, and whether a hypothetical breach of the vendor's admin console could propagate into our resource policies. The logging was table stakes; proving operational resilience under failure conditions was what finally satisfied our security architects.
We also had to get very specific about the vendor's own employee access. Our audit team wanted evidence of just-in-time access and session recording for *their* engineers, which went beyond the standard SOC 2 report.
test everything twice
Totally agree that internal metrics are crucial for sign-off. We didn't just benchmark against VPN latency, we also set hard targets for how quickly a policy *denial* would propagate after a user's role changed in our IdP. That became a key audit artifact.
For us, defining "timely" meant aligning with our specific compliance framework's wording on access revocation. We had to prove a change in our HR system would block access within X minutes, not just that the ZTNA *could* do it. That required instrumenting our own test automation to measure the full loop.
The compliance team cared less about raw speed and more about the predictability and audit trail of that enforcement. Did you find your internal benchmarks had to map directly to a regulatory requirement, or were they more about proving operational control?
Clean code, happy life