They use a blockchain for payments based on resource use, but not for anything else afaik. I have not seen details on how routing is performed, how data redundancy is maintained, how nodes are elected to perform DNS duties, how DNS is performed, how their censorship voting can be accomplished, etc.
I have been reading through the reddit pages and trying to glean more info, but it seems like people there only have the white paper to go on. White paper is here: https://www.google.co.uk/url?sa=t&source=web&rct=j&url=https://substratum.net/wp-content/uploads/2017/12/Substratum_English_Whitepaper.pdf&ved=0ahUKEwjFiqKX-KfYAhXnLcAKHZrOBZUQFggwMAE&usg=AOvVaw263PHC4BdfxtB99qkziE7t
Apparently, the custom DNS will route to active nodes using HTTPS. However, I haven’t seen any explanation of how HTTPS certificates are purposed and if sites resolve from regular DNS names, it would seem easily subject to censorship. There are no details on how DNS is done, how it is distributed, which nodes can do it, etc, afaik. There is no mention of namecoin or anything similar in the white paper either.
I also can’t see how data is duplicated or deduplicated and there is no details on caching mechanisms or how it may scale with demand. We don’t know how the data is secured either, other than encryption being used.
There was some talk of substratum being like a distributed VPN by some, but this seems incorrect. The white paper suggests it can replace Tor and VPNs, but in detail, it just means data on their network will not need a VPN, as they claim the routing will be firewall resistant. Without more info, it is hard to say either way, but from as no new software is said to be needed, we have to assume DNS will be the first weak link, followed by HTTPS man in the middle attacks if certificates are not issued (how can the cert agency vouch for the nodes?).
There has been no source code released yet, but some have said it would be released after the beta. The beta was due Dec 2017, but looks to be delayed until early 2018.
However, their market cap is now over half of of maidsafecoin and their Google trends activity is probably 20 times that of maidsafe. Saying that, SiaCoin, Storj and SkyCoin are also ahead of maidsafe is Google trends, with maidsafe not really catching hold.
I remain convinced that SAFENetwork is far more advanced. It is already open source, there have been many test nets and now 2 alpha nets. SAFENetwork still needs to prove it can work in the wild with fully distributed nodes, but we have even had test nets exercising that.