We have the former - it is very good - and big! - takes about an hour to built first time.. We have it on a play table so it is at eye level. DS3.5 stands on the table to reach the top. You wouldn't want to have to dissemble it oftrn there are lots of pieces to put together. It needs to be built, and stay built.
I would not pay £80 for it though - you can normally get it half price in the half term toys sales - I got it for £37.50 and it is a bargain at that price.
With the 20% ELC code though it is not bad value...
The good thing about getting the castle is that relations can buy all the bits and bob. We found that the ELC knights weren't that good - things broke off them and, as they aren't articulated, they don't do much. My DS prefers to play with the playmobil knights and horses with it.. and get a princess too!
Can't comment on the other one.