Zeplin doesn't do what Figma does, but Figma does what Zeplin does, if that makes sense. You wouldn't stop using Figma and use Zeplin instead, you'd only supplement your Figma license with Zeplin if you thought Zeplin did design handoff better than Figma (maybe it does, I haven't used it in years, but that wasn't the case a few years ago).