I think the downsides are due to the extreme centralization and that there is no protection of the private property of the users against the block producers and that there are many computer vulnerabilities discovered and probably to be discovered. There are also the departure of several executives in December 2018 and moreover its creator Dan Larimer, wants to join another project without claiming to leave EOS. But the advantages are that the EOS is fast and that it saves energy compared to traditional blockchains and there is also an easier implementation of smart contracts.