This work contains a great summary of many elements of Scottish folklore, but there are some areas where McNeil accepts the sources a little too uncritically. For example, I didn't find her discussions of the druids particularly enlightening, and there were several points where I saw a great deal of Germanic material and the author didn't seem interested in sorting Germanic from Celtic.
This being said, I found the discussions of magic, witchcraft, and fairy folk to be of interest and adding considerably to my knowledge in the field of folklore.
On the whole, though, this is a useful resource for understanding uniquely Scottish folklore. I would generally recommend it with the above reservations.