There are no real players in this mockup using GPO so there is no covering up.
Another ballet company up in the northwest used the GPO mockups for their ballet. It was cheaper than paying the royalty fees for the audio recordings plus we were able to change the tempos for their performance.
GPO was used to show what a small orchestra library can do without the costs of purchasing the larger libraries. I think that the Nutcracker proves the point that you don't have to have the huge libraries to get decent results. What you hear in the recordings cost $149 for the library and ARIA player. You can't beat that for the money.
I do use many of the larger libraries for my other work such as Vienna, ProjectSAM, Kirk Hunter, Sample Modeling and a few others. Even in my large templates, there is still quite a bit of GPO instruments. The woodwinds blend quite well with other libraries. I also use the Garritan Authorized Steinway quite a bit.
The best thing about the Garritan libraries is how well they work with notation programs. I've been using the Concert and Marching Band library in Finale for doing marching band arrangements.
I use the piano roll view for all MIDI editing. It's what I started with many years ago. I do use the staff view for recording live instruments and vocals.
Jim