In general IOStore should work just the same as pak files.
If you enable the creation of IOStore containers you will always get a pak file and it’s corresponding .utoc/.ucas files.
If you load the pak file in a project that had IOStore enabled when packaging, the engine will detect the utoc/ucas files and load them automatically together with the pak file.
However, some of the more advanced things possible with custom paks (e.g. changing the asset paths or the pak mount point) might not work for IOStore containers.