I have been looking at this useful site https://latinitium.com/best-books-for-learning-latin/.
The advice offered there about who should read Nutting is:
It is best to have a good grounding in Latin grammar and vocabulary before reading Ad Alpes. So, read and study Famila Romana, Fabulae Syrae, Fabulae Faciles, Epitome Historiae Sacrae before you start Ad Alpes.
I would have thought one reads Fabulae Syrae as one reads the later chapters of Famila Romana. Fabulae Faciles dont seem to me to be much harder than Fabulae Syrae and it seems to me that anyone who has carefully read Famila Romana would be well equipped to tackle Nutting. It would perhaps be preferable to have studied the extra grammar in Roma Aeterna before tackling it but I would not have thought it necessary to work through the whole of Roma Aeterna. I dont think anything could induce me to read the Epitome Historiae Sacrae.
I think that Jandar’s observations about Nutting being a transition from Caesar to Cicero need to be put in context. The preface says
"The student who passes directly from one author to the other is confronted simultaneously by three difficulties: (1) an unfamiliar vocabulary, (2) long and complicated sentence structure, and (3) thought and content rather remote from his own experience and very hard to grasp when the reading progresses at the rate of a few lines a day.
In other fields victory has often been won by dividing the difficulties to be overcome; and it is suggested that this successful policy be applied here by concentrating upon a single problem at the start, leaving the others for later treatment.
In pursuance of this plan, the present volume, which is designed primarily for use in the first half of the third year, concerns itself chiefly with the matter of vocabulary. Complexity of sentence structure is everywhere avoided, the thought is simple and directly expressed, and the units are so short that the pupil may hope to accomplish something definite at one sitting."
So Nutting isn’t really a transition to Cicero except in matters of vocabulary and only if one has read Caesar and only assimilated military vocabulary. There isnt much military vocabulary in Familia Romana so I am not sure that those who have read it would find anything really hard in Nutting.
I have only read the first chapter of Nutting and so stand to be corrected but the preface says that all the units are of the same level of difficulty. So the acid test would be to look at the beginning and see whether it interests you and you can manage.
The real difficulty of reading Cicero is the technical legal and political vocabulary and the cultural context. There are many good modern commentaries which can help with this.