I've been thinking a bit about the use of Mustafar as the location for Vader castle/sanctum. On the one hand, sure, part of it would be linked to this being the site of the most physically agonising moments of his life and where Padme died (or so he believed.)
If it we were just going by RotS that would be enough, but there's an episode of TCW that has me wondering if this place had greater meaning for the Sith even before Vader's duel with Kenobi. It's the site of Sidious's secret lab where he carried out experiments on infant Jedi hopefuls, in what we can only presume led to the likes of the Inquisitors. Possibly not a coincidence that in Rebels Kanan is said to refer to this place as "where Jedi go to die", which I interpret as foreshadowing of Vader's dominion here and probably where the inquisitors are trained and conditioned, most likely under Vader's direct supervision.
Could this planet be like Dagobah? A natural nexus of the force, only tilted or somehow corrupted to the dark side? Did the ancient Sith have a presence here? It seems the LFSG aren't done with this moon yet.
Speaking of moons (not space stations!

) I've seen references to Jedah as a moon. Did I miss something? I don't recall seeing a larger primary, either in Jedah's sky or the wider shots from space. Mind you, I could say the same thing about Endor...
You do bring up a good point about it maybe seeming jarring to me because they're mostly new locations. I wonder if I'd have felt the same if Cassian had met his asset on, say, Nar Shaddaa (which, while technically it would be new to the movies, is a very familiar location for fans of the EU).
Of course it's subjective, but I found on second viewing that it seemed to flow much better once I knew ahead of time what was going on.
P.S. Random side note, I'm sure I'm just slow and everyone else came to this conclusion right off the bat, but I was wondering to myself why they didn't include Wedge in the final battle along with the likes of Red & Gold leader. It's just now occurred to me that he was probably left out because of his
"Look at the size of that thing!" line in ANH. Had he been at Scarif he would already have gotten an up close look at the Death Star before they pulled out.
I also noticed in some behind the scenes footage that for the Yavin base scenes they did appear to have lookalikes of Biggs & Porkins. I can only assume the reason they didn't end up using Biggs is because they still have an eye towards the cut Toche Station scenes still being a thing that happened and if so, then Biggs wouldn't have defected until *after* Rogue One. Indeed, he probably got to Yavin less than a day ahead of Luke. As for Porkins...I don't know, maybe to avoid the inevitable jokes?