Looking at the website, it appears that in the first year, its not free. You have to pay half price for English Heritage sites.
English Heritage - Renewal Historic Scotland members can book their free visit on the English Heritage website. First Year Historic Scotland members should purchase an admission ticket and enter the promotional code HS50 to receive your 50% discount on tickets. You must take your valid membership card(s) with you when you visit
I always find these places quite busy personally and prefer the open hills and fells to spend a day if at all possible but thanks for the information on Historic Scotland, it will come in useful in the future I’m sure.