Fully cast zinc connectors are best used when living in a humid climate. Some steel connectors are galvanized and others are bare steel. The EMT is not intended for use in adverse weather conditions, but under the eaves, on the porch it is fine, but the humid or coastal climate will give it problems. In such situations, cast zinc fittings are worth the extra cost. I've used EMT light wall tubing in construction and in numerous businesses I own and rent for decades, but it wasn't until I retired