I only used Gleim sims on REG because they were required for my MBA class. And even then they were open book, the Gleim ones IMO were a lot harder than what I saw on the exam, then I never used them again when prepping for the exam. Personally, I do not like Gleim at all, it is unnecessarily difficult and crushed my confidence. But on the other hand, if you know Gleim through and through, the real exam will be a cakewalk.
For all sims, I only studied them on my third try on audit, and that was to only help me understand some concepts more, and it did. I'd say just learn the concepts however you can, if that is from sims, mcq, lectures, book, whatever, do that. But studying sims will not help you with sims on the real exam, the likelihood of you getting a sim that you have studied for are relatively low.