For something like t-butyl bromide going to t-butyl alcohol, there is no possibility of forming stereoisomers, so the question of retention or inversion becomes a non-issue.

That is a very interesting paper.

I would not say that the SN1 doesn’t apply to secondary alkyl halides *at all* but let’s just say they are much less important than they appear to be.

Let’s just say that the whole teaching of SN1/SN2/E1/E2 is pretty muddled, and has been this way for quite some time. If you take introductory organic you would come away thinking that organic chemists spend a great deal of their time trying to plan out SN1/Sn2/e1/e2 reactions whereas in reality the ratio of published SN2 and E2 reactions vs SN1 and E1 reactions is at least 100:1. Even then the SN2 is best done on primary substrates to avoid side reactions.

It’s a mess. I’m glad someone has gone back and looked through the original Ingold/Hughes papers, because they are the basis for a lot of what is taught.

You’ll likely only ever see HBr if you are performing substitution reactions on alcohols. The purpose is to turn the poor leaving group OH into the good leaving group H2O, and then, depending on whether the substrate is primary (SN2) tertiary (SN1) or secondary (ask your instructor, answers vary!) you will obtain the resulting substitution product.

I’m not sure what details you mean by “all necessary details”, but even a limited reading of that would neglect issues like stereochemistry, etc. So the answer would be no.