The different software models fulfill different functions

number.1 plays just monophonic sine waves

You can play all kind of tunes, switch into other octaves, play continuously different values, short or with a long release (what gives the "singing" touch.)

There are different types of scales, small range bends, adding attacks and 12 presets of ADSR envelops. Similar to the clarinet you can set the accidentals to play different keys.

As a special siren sound you have the chance to imitate the Theremin instrument