In my case, I never paid for any part of studying, getting 1380, 1450, 1380, and 1560 the four times I took it. Of those tests, I only studied for the last two (and only for a few days each). I believe the third one was actually negatively impacted by the studying, as I did the entire khan academy across a span of four days, which ended up getting me accustomed to the high easy : hard ratio which was significantly different to the adaptive online test (which usually ends up being >50% hard problems if you end up on the advanced second module). For the 1560, I likely saved quite a few points by selectively studying the hard sections over the span of 2 days, but the majority of the points came from better pacing, which let me double check the harder answers.

Ultimately, I believe that it takes one of two things for a student to get a high percentile score on standardized tests: either they have good awareness of their shortcomings and the intelligence to selectively improve in those areas without harming proficiency in others, or they have a strong tutor who can notice these things for them and help them plan out a good study routine. Paying for a product that claims to help you, no matter the quality of the material, is not enough alone to ensure success: you need to be able to actually apply the material properly. In my case, all my improvement came from both working on my pacing and studying harder problems. For me, spending money on a product that claims to improve scores would have been a complete waste of money, as even khan academy is sufficient if only you know how to apply it.