My DS17 took the new SAT this past spring. He is in H.S & took it at the regular time. The biggest problem with the SAT is the time pressure & the length of the test rather than material.
The new math section is both easier yet covers more material. The new test is supposed to cover anything through the Common Core Algebra II or Common Core Math 3 sequence. (Same thing) Keep in mind that by the end of Common Core II most of what used to be in a Trig class is supposed to be covered.
On the other hand the questions in the math section are less tricky than before. The questions are just more straight forward. On the old test a question might be 2 or 3 steps, or would be a more abstract question. On the old there might have been a grunt way to do it that would take a long time, but a clever way that would be fast. On the new test, the questions are just more what they seem at face value.
As to material.. Keep in mind that while Trig will be covered it will only be a few questions. If you are looking for a cutoff for DYS or other gifted program. Your time may be better spent on other aspects of taking this test. Like skipping over & coming back to problems you have no idea how to solve.
As to the reading & writing multiple choice section. The new test doesn't test for esoteric vocabulary. And the reading sections are more geared towards non-fiction. (There are social Studies & Sicence questions.) For most of us on the board the issue here is really speed.
I'd go over general tricks for taking this type of test. Guessing is no longer a penalty. But your child will do better on the SAT if they can answer the easy questions first, and come back to longer time consuming questions. Teach them to skim the reading sections, read the questions & then go back and read the section thoroughly before answering any question. There are often looking for the 'best' answer and not just the first one that fits.
The new test doesn't test for esoteric vocabulary.
I assume you don't need the essay section. I'd skip it and one of the nice parts is it's isn't the first part of the test anymore.