While I agree with much of this quote from Evelyn Underhill, and I appreciate the quote at the end from John of the Cross; she completley ignores the superior fruit, which are both ethical and chaarismatic, even while she quote a poem from John of the Cross on an OOBE. So, the quote only support a very week understanding of mysticism by Evelyn Underhill.
We should never forget: "We know a tree by its fruit..." Matthew 7:15-20 NKJV
You counseled me many years ago to be cautious of the over-use of intuition when making judgments- and I feel this is the same here. There is extensive evidence, if we use this book as our basis, that Evelyn was a fruitful contemplative. As I wrote earlier, there is evidence in this book she manifested all of the following:
1 Out-of-body experiences (she uses the terms "transport" and "rapture"- keep in mind Bob Monroe hadn't been born yet to create the term OOBE

)
2 Ecstasy (her explanations suggest direct experience- it would be difficult to describe them so well otherwise)
3 Spiritual joy (1st jhana)
4 Stilling of the mind (2nd jhana)
5 Opening of the heart (heart chakra) and spiritual tears
6 Spiritual crisis (awakening and Dark Night of the Soul)
7 Right discernment of teachers (her preferred authorities being saints John and Teresa)
8 Intuition (she refers to these as auditions, as automatic writing, and as the "call" to the spiritual life)
In my opinion these show very great attainment.

Especially when we read the ancient mystics and cannot establish the same quantity of fruit- we have to infer about them from the information that is available.
I put additional credence in her as this was also a book that was more or less given to me by the Inner Director to study. It has been a great discerner of teachers and authorities over the years, so I tend to defer to the judgments it gives me. It is the same Director that also showed me Jhanananda.

Unless- have you actually encountered Underhill in your adventures in the spirit (OOB)? And have seen that she was a solely intellectual figure firsthand?