As a music composer who loves scoring fantasy soundtracks, these keys are extremely useful. The sound quality is great and there are no bugs as far as I've used it. The only thing is the no Harpsichord changing or coupling registers, but I suppose that's something I can live without.
The recorded samples are full and bright, and help the instruments' characteristics shine. Note: most of the pianos appear to have upper limits to F7, rather than C8. Also, they seem to be balanced similarly to their real-life counterpart (as such, they're a bit quiet).
Buyers beware: the harpsichords have no option of changing or coupling registers. Regardless, the sound quality is good and it's more than worth it for the pianos.
All harpsichords are great, the Austrian Harpsichord has a limited range but it's nice overall. All the pianos also sound nice and have a very nice timbre.