TLDR, we're working on updating and reworking the consumables for Version 0.14 but I'll explain why they are the way they currently are.
The Ultra Sense is the 'when you know what's coming', that's usually the best time to use them. Otherwise it's a hail-mary play which usually is the kind of play that could win you the game.
During playtest, if allow players to use it after a card is selected, they essentially become invincible if they have the right consumables because it's a get out of jail free card; the answer to that would be to lessen the amount of consumables you get, which then makes it very valuable and would end up never being used (like item hoarders in RPGs, only using their items at the final boss).
We want to provide players a way to mitigate attacks against them without it being a no-brainer way of plowing through matches that are way above their level. There's a satisfying feeling when your consumables does land and reflects damage or activates ultra-sense but we do understand it's also a bad feeling to use one and waste it.
We're looking into adding passive activations where it would provide you protection for multiple rounds of a match in exchange for health or ultra-sense activation or something. There's not a lot of variables that can be changed so we'll try our best to come up with something within that realm.