I recall Bishop Williamson having noted this was "worth reading."
My impression at the time was that:
1) The manifesto was very good in identifying the dehumanizing aspects of industrial society
2) But was always just a bit off on the moral side
3) Because of his atheism
4) And it was precisely this atheism which skewed his moral compass
5) In such a manner that his intellect was good, insofar as he accurately perceived the cause of the problem (the dehumanizing effects of industrial society)
6) But unaided by the religious conscience and the moral judgment that rightly formed conscience elicits, he adopted an "ends justifies the means" course of action
Which is all another way of saying that, had he only been Catholic, he might not have become a murderer, and the good points he made regarding industrial society's impact on man would not have been dismissed because of his low moral character:
God never entered into his calculus or worldview, except insofar as it was perceived as a Marxian-like "opiate of the Masses."
That's how he ended up a killer.
But for 85% of the Manifesto, it is, as His Excellency said, "worth reading."