Free subscription to subset of targeted customers?

Hello IH friends. Struggling to acquire customers, has anyone offered free subscriptions to a niche group in their targeted customer base? Any horror stories or 'gotchas' to watch out for?

Did you offer it free for [six months, one year]? Did it then convert into a paid subscription?

I KNOW my potential customers NEED my SaaS, but I've been falling flat on my face with acquisitions.