Mibba is very easy to use and navigate, and it has a good amount of members, but honestly the admins ruin it. I was on the site for six years and I would always see moderators and assistants abusing their power left and right, and they would pick fights with other members and then permanently ban them. And I'm not talking about little fights about the rules - they would insult writing, take journal entries and articles down because they didn't agree with it, accuse writers of plagiarism for having similar stories, etc.
Even as a regular contributing member to both articles, stories and journals, I got banned. I was told it was temporary for being a little rude to another member (Which I was, I'll admit) and then ten months later I find out it's permanent. When I ask why they changed this, they said because they could and there was nothing I could do to change it. Considering I was a member of five years that NEVER got in trouble, it's pretty absurd to get banned for calling someone stupid (Yes, that's the extent of my rudeness). ESPECIALLY when I wrote the admin a few days later apologizing for my behavior.
Long story short, the admins and mods treat the members like garbage. So as long as you plan on talking to NO ONE and only posting your stuff, then sure. Join. You'll get some good traffic and and it's easy to use. But keep in mind that the staff is incredibly rude and you should keep to yourself.