Have you seen it in person yet? I don't have a vanity pm, and have no desire to own one, as I found it small. I wouldn't call it a mini bag, more of a smaller crossbody. It's a pretty underwhelming bag imo, don't really understand the hype behind it.
From what I can remember, I was able to fit my phone, compact capucines wallet, car keys, and I squished in a 5"x7" pouch. As long as none of your slgs are thick/overstuffed, you should be able to fit all of them. I own a lot of bags that are roughly the same size as vanity pm, so I didn't want to get another one in a similar size. If you don't own any small crossbodies, the vanity pm will be a gamble for you. I think you'll either be ok with the size, or you might hate it when you realize you can't fit some extra things. I don't regret any of my small crossbodies, and they're still my favorite bags to own, just some days I wish they weren't so small.
I think the biggest con about the vanity is that when you actually fill the bag, it warps in a not so nice way. The weight of the bottom section drags down, because of gravity, so it makes the top look like it has a bulge or a hump(?). I don't really know how to describe it.
If you love vanity-style bags, I would consider Chanel. Chanel's vanity bags have more of a rigid + supported structure, unlike lv's soft canvas. You can fill and use a Chanel vanity without the bag looking misshapen. There are A LOT more vanity choices than Chanel's website shows, so if you're considering, I would go to a boutique. Other options are
Coach Trail Bag and Hunting Season Trunk bag, which are pretty similar to the vanity pm's silhouette and dimensions, but both are hard case and at a fraction of the cost.