No, unlike Tor and p2p it's a decentralized network where no single user maintains the content at any given time. Note: An easy to use Tor browser is also available if you so choose.
Truly anonymous uploads, downloads and postings?
Yes provided you don't make simple mistakes such as giving information about yourself. Just follow the steps provided.
Free speech internet?
Nothing is moderated nor removed from the network. This includes message boards, site pages and content.
Connection speeds in visiting darknet?
Depends on the amount of time you allow your connection node to mature and of course your providers speed. But in short, you will have generally slower speeds through the network then standard internet. True anonymity has it's price.
History? Is it fully tested?
Darknet is a network thoroughly developed and running for over 10 years without a single network security breach. Thousands of users continue to share content and ideas daily.