If it’s a good opportunity, rare in your location, at a reasonable cost, I’d take advantage of it. It probably shouldn’t be the last prep for testing a year from now, but it can set some base principles, techniques, etc. in the brain to sink in and stew around for a while. Studying next year before the actual tests will be easier the second time around, with more retention as it’s not brand new.
IMO, that’s way too late to be taking an SAT/ACT for the first time. Fall of Junior year and then Spring, with Fall Senior year only as an emergency backup is my preferred plan (and many others, based on discussions here). That allows time to get results, see what needs to be worked on, focus on those topics, etc. Waiting until Sept. of Senior year only leaves time to get results and rush preparation for one more shot.
If the student is currently in Algebra 2, all the material will have been taught by then. Same with the grammar/reading topics on the tests.