Reddit Ads for a small B2B test: community targeting or keyword targeting first?

Say you're a B2B SaaS with a $30/day test budget and you want to know whether Reddit can bring in demo signups at all. You can target communities (specific subreddits like r/sysadmin) or keywords (matching what people type in posts and comments). My hunch is that community targeting is the better first test. The audience is narrower, so if the campaign underperforms, you can tell whether the message or the audience is the problem. Keywords give you more reach, but they're noisier and can drift into threads where nobody is buying anything. The counterpoint is that smaller subreddits can run out of inventory fast, so the test might stall without spending much. Has anyone run both on the same offer and seen which one held up past the first two weeks?

A narrow audience doesn't make the result easier to read, at least not at $30 a day. A small subreddit might only serve a few hundred impressions a week, so zero signups tells you almost nothing. With that little data you can't tell a weak message from a dead audience.

Keywords are noisier, but they spread the budget enough to show whether anyone clicks and signs up at all. From there you can check which threads the converting clicks came from and build your community list off that.

Keywords don't fix the signal problem, though. At $30 a day, either setup will probably get you only a few clicks a day, and demo signups are rare enough that you could see one or zero in two weeks no matter how you target. So the signup count will mostly be noise. For the first two weeks I'd judge it on the step before signup, CTR and time on page, since those move fast enough to tell you whether the message lands. The converting-thread idea still works, but build the community list from a handful of clicks and treat it as a hypothesis.

I'd be careful with CTR as the early read on Reddit. A lot of clicks there come from curiosity or accidental taps on mobile, so a high CTR can just mean the headline is catchy while the offer isn't relevant to anyone. Time on page has a similar problem, since it mostly reflects how fast the landing page loads on a phone.

A step closer to intent works better, like a pricing page view or a scroll past the feature list. Anyone who gets that far has a reason to be there, and the event fires far more often than a demo signup, so you'd see a signal within days. The catch is that you need to confirm the pixel actually fires on those pages before trusting any of the numbers.

Do you have a pricing page on the landing site, or would the test send people straight to a demo form?