It is a platform where you can upload work and receive reviews and feedback, being able to improve the work, in addition to being published in PDF immediately
I uploaded a paper on a communication studies theme that had been rejected by a journal. I received nine (9) evaluations ... averaging to 4.6 on a five point scale. There were some suggestions for how I might revise the paper. So ... there is the question of the reviewers - there was probably a mix of established and younger researchers offering evaluations. There is the question of the quality of the feedback - as above, some suggestions were offered ... and some did give me a valuable viewpoint to consider, but others/most were fairly broad and non-specific. There is the question of the what the assessment average means - as above, my work generated a very high average ... but the paper had been rejected. I have revised and submitted to another journal - still undergoing review. I guess my conclusion is that it is a place to get some additional viewpoints on your work, but what you get is fairly limited in scope and quality. Looking through the participant list and the range of papers, it seems heavy in physical and medical sciences and very light in social sciences. I, however, did not opt for the 'paying package' ... I question whether there would be value in paying for it.