Does Unigine have a more efficient source code than QuestViewer does?
In comparison, Questviewer has always been a bit of an odd engine developed by a very small team if I recall correctly. It was very hard to understand for newcomers to use this software due to a lack of a proper developer community. Its workflow was vastly different than other game engines. For example, there was no ctrl+z feature in it. Yeah, you had to do everything right in one go. That's one of the reasons why the ShipSim games became increasingly harder to maintain, because less and less people knew how to work with it.
Then there's Unigine, an engine that was developed much more recently and thus utilizes the potential of modern systems far better. There's also better documentation, though not in the same league as Unreal Engine, but from what I understood at least enough material to work with. The engine seems far less technically limited. The jump in graphics will be the first thing people will notice.
What that will say for performance, I cannot tell though, as I've always seen Nautis run on VSTEP PC's. A modern engine doesn't automatically guarantee a smooth game or sim. Hence why an Alpha is quite welcomed in my opinion.
What I wouldn't be surprised of, is that Nautis Home will generally run a lot more stable, with less of those odd errors and crashes that SSE was plagued with. Time will tell.