If you do not trust the MIDI enhancer, open the monitor window. It will monitor the harmonizing note and the pitch offset. The pitch offset is added to all notes equally. If it enters a critical range (which can lead to errors), it will be drawn light red or inverted.
It also shows you MIDI errors that ocurred. If you play very fast (many notes together) and/or send many controller changes, it's easy to produce errors. The limiting part is the MIDI output interface of your computer. The MIDI Enhancer in general produces more MIDI messages on its output than it receives on its input. If on the input events appear with maximum MIDI speed (31250 baud), the output will already be overloaded. A typical error, or more a warning, is "note overflow" in pitch bend mode, which occurs when you press more keys on the input channels at a time than output channels are enabled. In that case the MIDI Enhancer itself switches the oldest note(s) off to limit the number of output notes (= channels in pitch bend mode).