Hi Elaine,
It doesn't have to use 3 fingers only, you can elaborate more on that using your 5 fingers to trigger chords, and if you get used to the tricks, you can sound very convincingly.
I use it on 'AI Fingered' mode, and there is a lot of flexibility in it.
For example:
If you hold C E G C, bass plays only the root note that in this case is C.
If you hold C F A C, bass will still play C because you have it in a octave, which can be useful in some cases (sounds like F Major over C bass).
If you hold just E C, while E is the lowest note that you're pressing, it will play C major over E.
And there are many more examples like these, experiment yourself and see how flexible it is.
Cheers
Valentin