From what I can see the Stronghold is pretty much in the right region. It's worth its cost. Could maybe use the extra hits given its early departure in most fleets. The Bastion is terribly overpriced. A good 30 odd points. It's not a bad ship, but just way expensive. I have not tested the other one, but my objection to it is that it shouldn't exist. It uses the same model as the Bastion but has a completely different profile, including reduced hits. This is absurd. Nate's "logic" was that he made the Bastion's stats before seeing the model and upon seeing the model thought it was too small to justify 8 hits. He also wanted the Demiurg to be able to field a ship in the cruiser clash scenario.
In the first instance I think he's wrong. The model seems to be quite clearly on a par with an Imperial or Chaos cruiser to me, in terms of displacement. They're not small at all. Grey Knights Strike Cruisers on the other hand have a much harder time justifying their 6 hits, particularly when compared directly to the standard SC.
On the second point I absolutely think it's unnecessary. Cruiser clash is a beginners scenario and the 185 pt restriction is for beginners, which really should be using IN/Chaos in the first place. Looking a little further into the scenario people have the option to remove the point limit on cruisers or simply select cruisers up to a set points value. So if you're a beginner, learn the game with standard fleets. If you're not you can simply modify the selection restrictions to allow for more diverse ships, enabling the Bastion to be taken.
So, given this, I haven't even considered the new Demiurg cruiser. If FW ever make a smaller Demiurg vessel then I'll revisit the stats. It's not likely that they will though.