[dasmoth]

One thing that isn't entirely clear from this post is whether the software works. The unimplemented-functions thing doesn't sound wonderful, but I'd still argue that there's a world of difference between software that blows up the moment you look at it and something that's pretty much working except for a few loose ends where a relatively obscure feature hasn't been finished off yet.

In the former case, demonstrating that what they've done isn't "pure genius" shouldn't be too hard.

In the latter case, I think that -- especially if this is something you need reasonably quickly -- there's a good argument for focussing on value delivered and fixing actual, observable, bugs rather than spending too long worrying about the internal details. If need be, it can always be quietly rewritten once the dust has settled.