Can I use big company logos on my landing page if an employee just tried the free trial? I will not promote

Hi everyone, I run a SaaS with a free trial. Recently, I noticed some pretty interesting signups using corporate emails from massive, well-known companies. They signed up, tried the tool for a bit, and left. No purchase, no upgrade, nothing. Technically, one person from each of those companies used my product for an hour. Can I legally (or ethically) put their logos on my homepage under something like "Trusted by folks at..." or "Teams from these companies use our tool"? Or is this a massive red flag that w