It will return a single line of output with 'JET3' for those files produced in Access 97 format, 'JET4' for those produced by Access 2000, XP and 2003, 'ACE12' for those produced by Access 2007, or 'ACE14' for those produced by Access 2010.
Access changed its format between Jet 3 used in Access 97 and Jet 4 used for Access 2000 and XP. The nature of the changes included moving the page size from 2K to 4K and added support for unicode. MDB Tools actively supports both formats. Newer version are very much like Jet4.