De-aged Anthony Hopkins was more than passable on Westworld, and they did that with a fraction of Rogue One’s budget. My guess is that the real problem is that they overuse Tarkin. The tech is definitely there to pull off this kind of thing in brief segments.
He’s in several scenes. And, IMHO, it looks great. However, it’s certainly not perfect. I had more of a problem with the voice work than the CGI. It doesn’t totally sound like him.
On the other hand, I’m now very intrigued as to who this other cgi character is.
I would assume he means Leia.