There isn't much trust from anything Mercola, he's to controversial and by his own admission not an water filtration expert
Much of these big box stores that sell water filters for either water faucet or pitcher style are designed for clean water only, the filter taps for the faucets are designed for pressurized lines to push the water through the filters, if power is lost for a good period of time the homes will lose tap water making the filter taps useless. Getting something like a Berkey or make your own Berkey can be used in the home or in the field, abit slower but more reliable and flexible and the filters last longer.
FYI, Mercola filters are made by Aquasana, just purchase Aquasana and one might save a ton of money if one wants to go that rout