Feeder frog is one of the more nutritious feeders you can feed your fish. These frogs are small even in their adult size (They don't grow into bullfrogs and they are not young bullfrogs). These frogs are generally darkish in colour while bullfrogs are lighter colours even when young.
On thing to be careful is if you feed all of them into your tank at once, some of them may be able to make their way to above water levels in the corners where it is harder for you fish to eat them. If you have arowanas for example, they could jump and hurt their barbels, leading to fractured or crooked barbels.
If you want to feed them out asap, you should throw a few in at a time, so that they have less chance of escaping your predator fish once they hit the water.
If you try to keep feeder frogs live, you should not have them floating on water. You should just give them enough water to keep their feet wet. If water evaporation is high, you should give them more water but provide them with pebbles to climb on. If you put too little water, you could fail to top up the water evaporates fully. If left on a dry surface for long enough, the feeder frogs will die and stick to the bottom of the tank and guess whose job it will be to scrape them out?