Mineral (metal) systems are not well regarded around here. Nature2 is silver and copper. Copper can kill algea but not bacteria, silver can slowly kill some (but not all) harmful bacteria. Neither helps get rid of bather waste and other stuff that gets in the pool so you must have chlorine along with Nature2. Both copper and silver can stain a pool and copper turns fingernails and blonde hair green.

So... it seems to me that mineral systems such as this are at best money poorly spent and can lead to staining and poor sanitization.

SWCG is a popular way to chlorinate that many people find convienient. I can't help you asses the risk to the cover but I would think in Maryland you get pretty regular rain and that would help dilute / wash away any salt from the cover.