What is the difference between KeyControl 49 and KeyControl 49+?

KeyControl 49 and KeyControl 49+ are virtually identical in their functionality. Yet, while KeyControl 49 requires a driver under Windows Vista and Windows 7 (its installation is described here) and might not fully work under Windows 8 (as explained here), the successor model KeyControl 49+ does not require a driver at all and works under all Windows versions directly after connecting automatically (as described here). Both keyboards can be used without driver under Linux (check here) and Mac OS X (see here). In order to identify which model you have, you can see if there is a "+" symbol printed on the top right side right behind the KeyControl 49 logo.