This tutorial compares the two After Effects extensions TextExploder and Decompose Text. They both can split a text layer into one text layer for each individual character, word or line. In addition, TextExploder can also isolate a single word or do custom splits with regular expressions.
But the biggest difference is that the text layers generated by DecomposeText always still contain the entire text and some expressions then make parts of the text invisible. This has some undesired side effects, for example that the bounding box of each layer still includes the entire text. Hence, individual layers cannot be selected or manipulated easily. In contrast to that, the text layers generated by TextExploder are normal text layers without expressions and with correct placement and bounding boxes. This is a big advantage of TextExploder. On the other hand, TextExploder cannot explode texts properly if the size or kerning of individual letters has already been modified. Hence, it depends on the task at hand whether you better use DecomposeText or TextExploder.