Musicnotes.com is offering software with which you can download and print sheet music and guitar tablature from their website. The software is free, some (I assume public-domain) music is free, most (I assume) music requires some sort of payment.

Does anybody have experience with this? Does it work well? What does the music typically cost? How good is their tablature? Can it be used for any purpose besides downloading THEIR music? For example, can you—
Create your own music?
Download from other sources?
Import MIDI files?
Create MIDI files?

I am reluctant to install anything, even if it's free, without a recommendation.