Really like this mic on different sources. Use it a lot on vocals (mostly in combination with any other dynamic or condensor mic), sometimes on percussive stuff or on BV with a lot of distance/room to create a different sound. Prefer the the 520DX over the Superlux D112 C, although the Superlux is much cheaper. There was always something in the frequency range (high mids) I did not like with the Superlux. If you are looking for something extra, with a perfectly balanced narrow frequency range, this is the thing. For me, a mic like the 520DX works a lot better than EQ-ing a 'standard' mic on a pré-amp or with a plugin in your DAW. Just set it up next to another mic, check the phase and your done.
No experience with harp however.
PRO: nice in combination with other mic's for a ton of purposes. Great built quality. Great value for money.
CONS: have to drive it hard on your pre-amp. Little noisy, but that can also be a benefit for what it may be used for. It has no shockmount. I use a Rycote (or an MXL).