Swim lessons. ISR or typical lessons.

My son is 15 months and we have had him in swim lessons for about 2 months. He’s up to a 7 second breath hold. Which is okay I guess but I’m not sure that it’s really necessary. He isn’t really kicking and he kind of just goes with the flow in lessons. Doesn’t hate it, doesn’t love it. Not sure if he’s learning anything.

My question is whether there is any evidence that ISR is safer or better in any way than typical weekly swim lessons. These swim lessons could take until age 2-3, maybe longer until he can actually “swim”. These ISR lessons seem to truly teach survival but can those children swim either? Idk.

I’m looking for any advice regarding swim lessons for toddlers. It is vitally important that our son learns to swim. Should we wait until he’s older? ISR? Anecdotes welcome. Links welcome.