An "outsider" thing? I've used it quite extensively and understand its nuanced differences from other offerings. That said, its a fancy messenger app that is a huge battery hog, and crashes and lags constantly. It's not really deviating from the image that it's built by frat-boys.
One thing I do admire about it is that it deletes the content. This allows me to be more "free" and take shitty pictures of myself just to utilize the fun parts (videos, stories, object tracking / emojis, and lenses).
But in the end, I find myself wanting to create content I'd want to share with my Facebook network. Sure, it's ephemeral nature allows me to communicate freely with closer friends than on Facebook, and in a more immediate sense, but I don't see how this is any different than any other messaging app with fancy "message format" features.
Except it deletes content. It feeds into the insecurities of today's youth, and shelters them from consequences of their own actions. Of course it would spread like wild fire. It's the safe space that college students thought Facebook was before people realized everything stuck around forever.
So outside of the funny lenses and stories, the main attraction is deleting content. So either your insecure, or you're sending dick pics.
I expect to be outspoken about this, but its simply my take. If you disagree, you can respect my opinion by not down voting me for it.