I was looking over scale on the ship... Personally I'm saying it's to-scale but the few refs I've found (which I think are not accurate and are #'s being made up in someone's head without any investigation/estimation) put it undersized.
Anyway, what I have found is that the astromech in the back is a Q7 model Astro... I'm not making this up. It's a sphere. My guess is it's essentially a "Torture Droid" astromech. A hovering R2 head, and I think it is supposed to be smaller... It's nto supposed to be a "full" droid like R2 though.
On the issue of scale, I'm saying the ship is to-scale... Being a CGI model there's no good reference to go with and the length I've read is to me clearly inaccurate just by eyeballing the ship, the cockpit, etc., from the film and still images of the CGI model. "scale" being off in books isn't uncommon for SW though. Almost every source still lists the Executor at 12km long, and AT-AT's at 15m tall. Both, very VERY off. And those have friggin' physical models to go by... CGI ships like this are even tougher. So I say it's right, kudos to Hasbro for using physical images to base their design on though, and not trusting books.