Kidpool has a strong enough activation that I'm fine leaving him in play for a while, unlike some other 'Pool allies. Trading 2 pierce damage for an acceleration icon is generally in your favor, though it does take many turns to earn back the initial 3-resource investment. If your collection is large enough, there are still probably some basic allies that would be more powerful to play. If you want to lean harder into the 'Pool aspect or are going for the "bad icon" archetype, Kidpool is definitely fine to include.