Tony Duff seems to like to make a big deal about how other translators are often mistaken and his translations are better. However, having read some of his translations, and knowing a bit about the issues involved, I've noticed occurrences of terminology and interpretive choices which he favors that are just as open to criticism as those of any other translator. And some of his interpretations are quite controversial. For example, he wants to read Maitripa and Milarepa as being proponents of gzhan stong.
I seem to remember hearing this from someone else. Personally, I have only so much as heard of Duff's name. But I was
thinking that "Wisdom Guru" sounds a bit too literal for a translation of Yeshe Lama in this context; since the aim of the text is (ideally) enabling one to attain the unexcelled stage of Dzogchen realization called "yeshe lama," translating it as "Unexcelled Wisdom" or "Highest Wisdom" would seem to make more sense to me... even if the guru, the state of Dzogchen, and the realization of that state are all one in the same ultimately.
As far as reliable vs. unreliable translations of Yeshe Lama, I was present at Tashi Choling once when Sangye Khandro & Lama Chonam asked us not to rely on their first translation of the text because they felt it somehow wasn't up to snuff, and they asked us to wait until their revised translation comes out (which of has since happened). I think maybe people who are saying their translation has some flaws are mistaking this latest version for the original.