The idea is decent in theory, but not in execution. The idea is that token staking is done by node operators which makes it much harder to pull of 51% attacks as it requires hundreds of euros in money to be put aside. It also protects against poisoned nodes, which is theoretically possible on something like Tor because of how easy it is to spin those up for cheap. Besides that the token also funnels a tiny amount back towards the developers in an anonymous way that would help them during development. In practice though they should have just went without the blockchain. I have been very interested in Session but their blockchain model was always one of the biggest things that might kill the whole project.