Depends on what you mean by the same:
- Yes it's the same, it defines the IOR of the reflections. If you are looking for the equivalent to "Fresnel IOR", then this is the one.
- No it's not the same, as it also defines the IOR of refraction (because any real world material only has one IOR affecting both reflection and refraction, not two IORs like the old Legacy Material)
- No it's not the same, as it only goes up to 3 (because real world non-metals don't have an IOR of more than 3, even though the Legacy let you use up to 999, and now the Physical Material has Metal or non-Metal modes)
- No it's not the same as you can't set it for metals, it's preset, unlike in the old Legacy
- And overall in the material, it's not quite the same as there is a Clearcoat layer with its own IOR, which didn't exist in the Legacy Material, so the overall reflectivity of your object may be different than just the Base IOR / Legacy IOR)
Set IOR to 1 for no reflections, yep. You could set Roughness to 1 too but I think that's redundant when IOR is 1. You wouldn't zero out IOR because it doesn't go below 1 :)