I don't know an awful lot about Brittas, but I looked on their website and found this:
BRITA Partner kettles use the BRITA filter cartridge to remove limescale, chlorine and heavy metals such as lead and copper to improve the taste, smell and appearance of hot water for beverages and for cooking.
Any good dechlorinator should obviously remove chlorine, and most of them will also get rid of any heavy metals present in the water, so I don't see why it would be necessary to use such thing. Normal tap water, once it has had dechlorinator added to it, is fine for use in 99% of cases.