И explore и open приведут к одинаковым результатам, но поскольку функция используется именно для того, чтобы открыть папку, то целесообразней будет использовать именно explore. Так код будет проще понять.

Parameters
...
lpOperation
edit - Launches an editor and opens the document for editing. If lpFile is not a document file, the function will fail.
explore - Explores a folder specified by lpFile.
find - Initiates a search beginning in the directory specified by lpDirectory.
open - Opens the item specified by the lpFile parameter. The item can be a file or folder.
print - Prints the file specified by lpFile. If lpFile is not a document file, the function fails.
NULL - In systems prior to Microsoft Windows 2000, the default verb is used if it is valid and available in the registry. If not, the "open" verb is used.

In Windows 2000 and later, the default verb is used if available. If not, the "open" verb is used. If neither verb is available, the system uses the first verb listed in the registry.