A piezo pickup will not be able to 100% replicate the acoustics and richness of a good classical guitar.  That’s why professionals always use a high-quality mic while performing or recording themselves. Some classical guitars come with a piezo-mic blend feature, like the SLG200N. Turning the mic pickup up lets you get close to a natural sound. Also, magnetic pickups won’t work on a nylon-string classical guitar. They only work with steel strings.