The NuShares method allows the equity of NuShares to be burned to eliminate the NuBits. This is essentially backing NuBits with NuShares as collateral. Intuitively, I think that you could consider that NuBits is backed by 100% of the market cap of NuShares, but I am not sure how this would hold up in a panic scenario.
This leaves us with two advantages over the Nubits/Nushares system:
1) Our bitAssets are backed with 200-300% collateral worth of BTS, wheeras NuBits is only 100% of its value in NuShares, I think. (I am really unsure about this point, however it seem clear to me that we have more collateral)
2) It is impossible to create "too many" bitAssets, exceeding the value of BTS collateral that backs them, because the system wont let you. However, if NuShares voters were not careful, it would be possible for the supply of NuBits to exceed the market cap of NuShares, and thus the NuShares 'collateral' would be insufficient to cover it.
Perhaps it is more correct to say that the %age collateralization in Nubits is equal to the current ratio between the market cap of Nubits and Nushares?
So if there is $4M of Nubits, and $8M of Nushares, it has 200% collateral. But if there became $16M Nubits, and still only $8M shares value, the collateralizaiton would drop to 50%.
Looked at in this way, the Nubits burning system does provide some safety, but not as much as there is in bitAssets. The system could still fall apart if the market cap of NuShares was not sufficient to support the number of NuBits that needed to be burned away in a failure scenario.
bitAssets are not completely safe either, if the value of BTS was to absolutely collapse to zero very fast, they would similarly become valueless, (they are like far in the money derivatives of BTS). However, they are much more safe than Nubits/Nushares. The Nushares system with burning is safer than the initial version without burning.