I like that book, very clear. Studying being allowed reminds me of a Fr. Ripperger talk where he mentioned seminarians trying to get out of studying due to Sundays, but not being allowed.
It is indeed clear, but Jone’s book is a distillation and summary of various schools of thought, with the majority opinions often presented as though they are the
only opinions. In plain English, I would advise, if Jone says “you can’t do this” and it is something you see yourself as
having to do, dig deeper and see if this is the universal or near-universal opinion of moral theologians, or if there is some “wiggle room” —
in dubio libertas.
There are also some times when I am just left scratching my head —
“huh? what did he say?”. Keep in mind that this book was originally in German (I think, may have been Latin), and was “Englished”, so something may get lost here and there in the translation. There’s also a curious passage where Jone allows an act of marital intimacy that you would
think would be one of the four sins that cry to heaven for vengeance. Don’t know
what he was thinking, and sadly, Jone is no longer around to be asked.
In short, Jone is a good reference, but it’s not infallible.