The DNL-DRM sounds more like an app than an ebook that would be readable on various devices? Can only be read on a PC? Mac? Linux? Do they have to be online to be able to read? You don't want to make things to hard ot restrictive for your potential customers.
2) It would probably work to lock things down if for no other reason than I don't think most people know much if anything about it (at least I don't think it's been broken). It's not that it can't be broken (any DRM can be broken), it's that no one has found it worth the effort yet (AFAIK). Of course someone can always take screencaps if they really wanted to capture the whole thing and put it out there.
Here's a bit from a post here a few years back...