I buy folio style cases, but mainly for the screen protection and not as a wallet. I do use the slots on occasion, like for transit cards during travel, but not regularly at home.
The problem with most of them is that if they're used as intended, as a wallet, the cover doesn't close properly with the added thickness of the cards. And when they are made to take into account that bulk, they have excess material that makes for a poor fit when not used as a wallet, and the slots are empty.
Some designs try to address the situation by incorporating a clasp, but it adds to the fussiness and bulk.
The detachable 2-in-1 style cases as pictured add even more bulk, by wrapping the wallet portion around a full case in itself.
They can be useful, but the execution makes them more tricky, and not universally appealing.