We often hear questions like that.

Here we would like to emphasize the key essentials of notation composer which justify the price compared to the freeware MuseScore Studio.

One example is the sound of imported MIDI files. Here you can find a complete summary not just about the sound.

Sound

Here are few sound examples of notation composer 5.1.0 vs. MuseScore Studio 4.4.4:
This comparison is made with the soundfont GeneralUser-GS. For MuseScore Studio, Muse Sounds are not used because:

• most Muse Sounds are not for free (the objective of this article is to compare notation composer with the FREEWARE MuseScore Studio)
• it is unclear if the few free Muse Sounds as of today will stay free forever
• Muse Sounds are irrelevant for the examples below
• Muse Sounds are not realtime capable

Guitar Riff

Guitar bending directly imported from a MIDI file: notice the bending at ~ 4 seconds of notation composer. MuseScore Studio ignores bending in MIDI import.

Panorama and Balance: this sample starts with left speaker and at ~ 4 seconds it turns to the right speaker.
MuseScore Studio does not offer pan or balance control. The sound is always in the center.

Dancing Music

Please compare at 3 and 10 seconds. For notation composer the rhythms echo and fade away toggling between the left and right speakers for a very dynamic sound. For MuseScore Studio these rhythms are static, with no kind of echoing nor fading away, nor any left to right speaker focus.
With MuseScore Studio this sound sample is 'flat' with a hanging tone at the end. The objective of the stereo movement of the sample does not come through.

Oh When the Saints

The glissando attack of the trombone at 0 seconds and 22 seconds is typical for this style of jazz song. At ~ 30 seconds the song fades out.
MuseScore Studio does not handle these sound characteristics directly given by the MIDI File. Even further due to an incomplete and wrong MIDI import, some instrument sounds persist and/or are de-tuned.

Rock Sample

The excellent more 'live' sound of notation composer is created by MIDI SysEx events with realistic 'fat' sounds and lots of pitch bends for the distorted guitars.
MuseScore Studio cannot handle MIDI SysEx events. MuseScore Studio in contrast sounds 'hollow'. The lead guitar with the characteristic distortion and bending is almost lost.