I haven't seen this book so I can't really comment on it, however from what you have mentioned, I don't really see what is so unique about the book.
It don't see any real benefit, in fact the following harms come to mind:
1. Masa'il mentioned in the lower categories would be automatically assumed to be weaker than those in the higher ones, when in reality, the complete opposite could be true. Acceptance - not authenticity- of a hadith in Sahihain could be disputed, while a hadith in another book could be backed up by Ijma!
2. If Moulana was not aware of a proof for a certain mas'alah, then he would have deleted the masa'alah or if he was aware of a "weaker proof" then the mas'alah would be relegated to a lower catergory, when in fact it should have been placed much higher up, thus giving the impression that it is "weak".
3. It creates the impression that these are the proofs for these masa'il, thus acceptance or rejection of them would be based on these proofs.
So instead of creating reliance in the mind of a student on the founders and Fuqaha of the madhab and mentioning the ahadith as backup for the masail, it instead creates the mindset that these masail are derived from these proofs. So if the proof here is weak, then the mas'alah is weak as well.
As I mentioned, I haven't seen the book, so I cannot "pass judgement" on it, however I don't agree with the system adopted for division of masa'il.
And Allah Ta'ala knows best