They have negative reviews from genuine users but suddenly all of them got lots of positive reviews in the last few days. It seems like a scam to get people to buy something.
Yes, for instance this one is kind of suspicious, most positive reviews are from the same day (11/8/2020) and include the keyword “bought”. He or she is not the only one making a paywall with demo decks in Ankiweb. This has been done for ages.