Neither are good enough (due to size) for more than eliminating some chlorine for taste. Rest of the claims are unsubstantiated due to a couple of reasons:
PITCHER FILTERS
Pitchers use GAC (Granular Activated Carbon)filters - Not enough contact with the filter in a “drip” type pitcher to reduce more than just some chlorine for taste. The reason for a top chamber in these pitchers is to slow down the water pressure to ensure more contact with the filter but it seems to be more of a gimmick than anything useful because you start with a filter that is just too small.
The longer the water is in contact with GAC filter the better, but GAC is composed of loose carbon granules, unlike Carbon Block which is a solid carbon filter that filters out more contaminants, GAC is not a reliable method at such small filter size to remove heavy metals, VOCs, etc.
It is recommended to replace these filters every 3 months for chlorine removal and one should stick to this schedule which makes these pitchers extremely expensive.
REFRIGERATOR GAC/KDF FILTERS
Refrigerators use GAC or GAC/KDF combo- Again too small to remove or even reduce the amount of any other contaminants but chlorine, therefore, you really need something like Reverse Osmosis Membrane with a sediment filter, GAC or Carbon Block to remove harmful contaminants: Fluoride, Lead, VOCs, radioactive isotopes, pesticides, herbicides etc…You get that from 4+ stage RO system.
KDF FILTERS
KDF Filter: (Kinetic Degradation Fluxion) Is a high-purity copper-zinc formulation that uses a basic chemical process known as redox (oxidation/reduction) to remove chlorine, lead, mercury, iron, and hydrogen sulfide from water supplies.
Filter Size and water pressure matter - the slower the water pressure and longer contact the better here.
GAC / KDF FILTERS
GAC Filter: Granular Activated Carbons are made using carbon that has been ground up and is held together loosely inside a cartridge or other container. GACs are best for removing odors, tastes, and chlorine.
Filter Size and water pressure matter - the slower the water pressure and longer contact the better here.
Tests were done with Brita filters, TDS (total dissolved solids) unchanged or higher due to most likely some loose carbon particles floating in the water from the filter. Brita’s KDF or GAC filters might simply be too small to be effective.
In addition, bacteria tend to build up in these filters since the filter is exposed to air, recontaminating the water which increases costs, decreases the quality and with most of the contaminants needing reverse osmosis to be actually removed, you’re wasting $ and aren’t staying safe.
Check out this page to see what exact contaminants are removed at what stage and what filter: Compact RO Water Purifier
Click Here To see the standard RO System GAC filter size in comparison to the pitcher.
BEST SOLUTION FOR WATER PURIFICATION AT HOME
REVERSE OSMOSIS SYSTEM
If you want to use your fridge for ice and to dispense healthy water: replace the fridge filter for a new one to stay sanitary, then bypass it with a Reverse osmosis system that’s installed under the sink and run a water line from the RO to the fridge. Clean, safe drinking water, for fraction of the price, needs filter replacement maybe every 2 years, membrane every 2–5 years depending on water quality, and you never think about your water again.
Here are two great choices depending on your handyman abilities:
COMPACT: Easy Install, smaller filters & tank: Compact RO Water Purifier
MODULAR: Fully customizable: 4+ Stage Custom Built Modular RO Under sink Water Purifier
COUNTERTOP WATER FILTRATION SYSTEM
GAC / KDF Chrome-Plated Countertop Filter System with Replaceable Cartridge
Or Green /Eco-Friendly
Eco-Carb Countertop Filter Unit With Cartridge - H2O-RCT-CP-CB
P.S Our crew is using 4-5 stage modular RO systems in our homes in California where the drinking water is not that great. It provides excellent water quality on tap. Also, it is the most cost-effective option out there. Because it will remove 0.0001-micron particles. RO system with GAC, Carbon Block and Sediment is your best way to keep you and your family safe from harmful contaminants.
The next level from RO is distillation but it’s too costly, all systems need electricity and remineralizing cartridges (replaced every 6 mo) to provide drinkable water. Otherwise, it's not fit for your main drinking water source.