This action will likely result in legal battles that go on for years, and the winner in court may or may not be Trump.
As I said above, the judge's stated preliminary intent to appoint a special master surprised me. She herself said the final decision has not yet been made and the DOJ may appeal. That said, at present, it appears more likely than not that a special master will be appointed.
So what exactly will that mean? Neither you nor I can now at this point, but allow me to share my admittedly speculative views here.
A special master will certainly have the delaying effect I believe Trump wants. But appointing a special master will not delay the entire investigation and the delay will be minor.
It's worth nothing the differences between this investigation and others Trump has endured.
This is a CRIMINAL investigation with a grand jury formed long ago and many witnesses already heard from. TRUMP"S track record of obstruction in this case is already well established and documented. A huge amount of documentary evidence already exists and has been thoroughly reviewed by prosecutors. Probable cause that crimes have been committed is already well established.
As far as I know, not a single witness has fought a subpoena or refused to testify before this grand jury. That often-used Trump delaying tactic has not been tried in this case, or if it has been tried, it has not been successful.
EXECUTIVE PRIVILEGE: Trump has frequently claimed executive privilege in his public statements and some defenses against subpoenas. But in this case EXECUTIVE PRIVILEGE DOES NOT APPLY. Executive privilege protects one branch of government (executive, legislative, judical) against the intrusions of another, like protecting a presidential aid from overreaching questions posed by a congressional committee. But congress is not involved in this. The National Archives is part of the executive branch, as is the DOJ. Executive privilege is not used to protect the executive branch from the executive branch, so, in this case, it simply does not apply. Accordingly, the special master's work is made that much lighter since the documents do not need to be reviewed with executive privilege in mind.
ATTORNEY CLIENT PRIVILEGE: This does apply. We can legitimately expect the special master to exclude all documents seized from Mar-a-Lago that are correspondence between Trump and his attorney's on a matter that is protected by attorney client privilege, or records that relate to the same. The DOJ filter team (a/k/a "taint team") is going through the documents now to isolate and keep those documents out of investigator view. Whether it is a filter team or special master, the work is the same and the delay would be equally long; except that, if the special master determines there is a need to ignore previous work done and start from scratch, Trump would gain a delay of the time that passed between the search and the appointment of the special master.
I'm thinking the chances are pretty good that the DOJ will simply accept and fully comply with the Judge's decision to appoint a special master. That nips in the bud the "legal battles that go on for years" you mentioned above, and frees DOJ to continue it's work without additional Trump-initiated delays. If DOJ does not appeal, Trump has nothing to contest, and the special master, who does not report or talk to Trump, can go quietly on with that work.
Again, my views shared here are speculative. I previously speculated that the judge would not take up Trump's case on jurisdiction grounds, and it turned out that I was wrong about that. I may be wrong about this too.