I used PrepScholar because they had a good value package which included the self-paced online course with a one-on-one tutoring package, where the tutor could view your online test results and go through them with you. It was not bad for the cost, however, if I had my time again, I would probably use a different course such as TTP.
Positives of PrepScholar included a diagnostic test to test your strong/weak areas, a customised structured course with modules to complete each week, tracking of performance against skill areas, the ability to set a schedule and study plan for yourself, simple and generally easy to understand content, and mini practice tests to complete and test your knowledge at the end of each module (which included working solutions in the answers). It would also get you to re-do modules if you didn't get a high enough score in the practice tests to reinforce the learning.
Main criticisms were the content was sometimes overly simple or lacked adequate explanations (I would often get questions in the practice test the content had not adequately prepared me for), only some modules had video explanations which meant a lot of reading, and answers to practice test questions sometimes lacked adequate explanations. You also could not access the "locked" modules, meaning you didn't have control over which modules you wanted to study outside of the weekly plan without requesting the admins to manually unlock them all for you. Additionally, several weeks after I signed up to the package (at the end of 2023), I realised the content was based on the GMAT Classic edition (I planned on doing the GMAT Focus exam), meaning I had wasted time doing irrelevant modules that weren't in the Focus edition (e.g. geometry, graphs etc.) - unsure if they've updated the content for Focus edition, but keep this in mind.