Why was it unusual for Jaggers to reveal to Pip that he thought the unknown benefactor's plans to make himself known were "injudicious"?
It is unusual for Jaggers to tell Pip that he thinks his guardian is making an unwise choice because he does makes it a point never to get personally involved with any of his clients.
Jaggers rarely gives a personal opinion on anything. He tries not to get involved, even with he does think that the people who hire him are not going in the right direction. He makes it clear to Pip when they first meet that he is only an intermediary.
“My name,” he said, “is Jaggers, and I am a lawyer in London. I am pretty well known. I have unusual business to transact with you, and I commence by explaining that it is not of my originating. If my advice had been asked, I should not have been here. It was not asked, and you see me here. What I have to do as the confidential agent of another, I do. No less, no more.” (enotes etext p.96)
Although Jaggers is basically Pip’s guardian, he makes it clear that he is not going to play a touchy-feely parent-like role. Yet he certainly thinks both Miss Havisham and Magwitch are making unwise decisions. He reminds him of this constantly, including as he is leaving right after explaining the conditions of Pip’s expectations.
Understand, that I express no opinion, one way or other, on the trust I undertake. I am paid for undertaking it, and I do so. Now, understand that finally. Understand that!” (p. 100)
So why then, does he finally speak up on the day that Pip is given his inheritance?
As I have told you before, I am the mere agent. I execute my instructions, and I am paid for doing so. I think them injudicious, but I am not paid for giving any opinion on their merits. (p. 196)
Pip is foolish with money, and just about everything else. He cannot take care of himself, and likely will waste this money like he wasted away all the rest.