To clarify who can and can't go to the Magic Realm: Every played sim can go there, including other occults and non-occults, children and families. It's just that any NPCs you may encounter will exclusively be spellcasters, and there isn't a lot to do for non-spellcasters unless you renovate the main building accordingly, which in its default premade state is just a big, empty warehouse with minimal furnishing, a few cauldrons and witchy collectibles. But you could, for example, place a picnic table outside and have a family picnic there with Cottage Living. I use Lilsimsie's Magic HQ in both of my saves, which is very cosy and even comes with living quarters for visitors staying overnight, but my sims mostly use the Magic Realm to buy stuff in Casters Alley.
Now for my personal opinion: As someone who has been longing for witches since day one, I can't even imagine playing TS4 without this GP anymore. Of course, no pack is perfect, and there were a few missed opportunities, like the spells being a little too tame (most of them are basically just flashier ways to do things sims could already do before), no career involving magic, and children can't use magic or even drink potions made by older spellcasters (mine can thanks to a mod), but does that ruin the fun for me? I think the fact that I own all expansions that come with residential worlds, and every single one of those worlds has at least one witch living in it, speaks for itself... o:)
