

I was just thinking about my experiences with MDPI (journals chosen by PIs, btw). Their managing editors gave a lot of proofreading & editing advice (free) and were extremely helpful & professional. Meanwhile, the big so-called "legit" publishers seem to leave that all to the unpaid peer reviewers.
I must add that I have no idea about MDPI's peer review process. It seemed a little light, but I'm not really qualified to judge the scientific aspects of some of the projects I work on, just the the evidence acquisition and the evidence synthesis methods. Wouldn't let a title like that slide though
I've heard mixed things
I've read that there is huge range from one journal to another with them, from excellent to non-existent