A scam
In short: a scam. Let me tell you why.
The textbook solutions they claim to have immediately available are not available. In order to get answers to the questions you have to make a request asking for them – individually. After having done this you also have to wait four hours before the answers become available to you. Thus if you want to get go through the answers following a chapter, you have to know which questions you want answers to four hours in advance. This asking-for-the-answers is a time-consuming process, and in a single chapter you may very well use up to 15 minutes simply clicking away manually on their website asking for which questions you want answered!
Most importantly of all, however, after having contacted the support team and asked them for a refund, on the third time of my asking they told me that they had indeed started the process of the refund and that I would receive my money within a week. After having been in contact with the customer service continuously since then – now over a month – they are now ghosting me and refusing to answer my messages.
If all of this did not convince you, I may refer you to the front page of their website. Here they claim that they have received positive reviews from 2500+ users on Google, Trustpilot and Sitejabber which – as you may have noticed on this website, simply is a lie. I would therefore tell you to stay far away from this website, since everything from their marketing to their products are lies.