There's no doubt that NUD is amazing. As for XCN, it might be amazing, but I'm still unable to compile on ubuntu.
I'm just not sure '1st mini-blockchain implementation'?
I can't find any information about why the NUD blockchain is smaller than a normal blockchain. They have one sentence in the announcement thread claiming to have a smaller blockchain and then nothing to explain why it's smaller. It's extremely unlikely they've done anything to significantly lessen the size of the blockchain. I don't even think the NUD code is open source so you cannot check anything they claim.