roop,The Superlux is a vocal mic in a bullet shell being sold as harp mic, not surprised the crystal mic sounds better for harmonica. Hell, IMHO the Superlux isn't a very good vocal mic, "SuperSux" would be a more appropriate name. "The sound you are now hearing is the Supersux suckin' quid from yer knickers."Checkout Youtube, look for "homemade" harmonica mic, there is a slew of them.
The Superlux is not a vocal mic in a bullet shell - I think you are referring to the Nady/Bushman Torpedo bullet.
The Superlux is actually a Chinese made Green Bullet clone, with a large diaphragm, High-Z element very similar to a Shure CM.
I have gigged one regularly for 2 years now and am more than happy with it. And yes, I have a Shure bullet with a White label CM and an Astatic JT30 with an MC151, so I do know what the classic bullet mics sound like. The tonal difference between the Superlux and the GB is noticeable, but nothing I would lose sleep over. I doubt the audience would notice.
Personally I think it's a very good harp mic for the price. Like any bullet, you need to cup it tightly with an airtight seal to get the best tone.