The obvious advantage of the split mold is that you don’t need an extractor to remove the sample from the mold. The disadvantage is that often the split molds will not meet the specs due to a small misalignment at the split. The split molds are typically more expensive than the solid. They are often used for “one-points” in the field. In the lab, If you are concerned about accuracy and consistency, it’s probably best to go with the solid molds and an extractor.