Here's a link that compares water filters, including Brita and Pur
Water Filter Comparisons & Reviews
The claims are that they remove chlorine and organic contaminants. That seems like activated carbon filtration. I see no reference to removal of Calcium or Sodium (or their salts).
The Brita site talks about chlorine, copper and organics, but not about hardness or salts.
Brita Pitcher FAQ: Frequently Asked Questions about Brita Pitchers | Brita
If you are primarily concerned with hardness, it seems they won't do much. If you are worried about chlorine (which doesn't bother me), then they do a good job.