Both are useful tools, but are for very different purposes and have little in common.
A CMA relies on ill-defined trends, while an appraisal utilizes comparable sales that can be validated by records. The appraisal verifies other factors like condition, amenities, neighborhood, and construction costs. The CMA will provide a non-specific figure. An appraisal delivers a defensible and carefully documented opinion of value.
The appraisal is produce by a licensed, certified professional who has made a career out of valuing properties and who has no personal bias or stake in the results. Although knowledgeable and helpful, a real estate agent providing a CMA potentially has something at stake since they get a commission based on the property’s selling price.