Which AI sourcing tools actually find better candidates vs. just being faster at finding the same ones?

I'm evaluating AI sourcing tools and the vendor demos all look similar. They all claim to use AI to find passive candidates we'd otherwise miss. When I ask for proof, I get case studies, not benchmarks. I'm spending £800/month per tool and I have budget for at most two. How do in-house recruiters who've actually deployed these tools assess whether the AI is genuinely finding better candidates or just automating what we could do on LinkedIn?