Both IAL and Oak leaf are 99% the same-they have antibacterial/fungal properties, help toughen fins/scales, ease stress, assist with longevity of the bubble nest, promote colonies of microorganisms, can slightly lower pH over time- to name a few good things the tannins can do for a fish.
As posted-the tanned water is what some hobbyist dislike-Too many leaves breaking down in a small volume of water can get toxic, however, as they break down/decomp-this naturally produces CO2 that can drive the pH down-making ammonia less toxic or converts it to ammonium-the damage occurs when you bump the pH back up with a partial water change or a top off with higher pH water.
The antibacterial/fungal properties can be killed in water temps over 110F
Since tannins are a natural product-you can't overdose it...Safe to use long term.
Tannins can be use for a general tonic, breeding, rearing/keeping fry and medication.