TheReviewIndex.com I didn't find to be very helpful, as it doesn't index all products and sometimes just refuses to check on listings you ask it to. It seems to have some kind of subscription model, but they don't list the price and offer some kind of enterprise model that doesn't sound like it has anything to do with checking reviews.
SearchBestSellers.com isn't for checking individual products, but it will show you the top sellers for each category so you can get an idea of what could be good in the category you're looking for
Camelcamelcamel.com is a price watch tool that will also show you some historical info on a product & notify you if you sign up and want to be emailed when a price drop occurs
There are a few others on AlternativeTo that weren't there the last time I checked. https://alternativeto.net/software/fakespot/
On Reddit, some people were mentioning alternatives, including asking ChatGPT about the product and it might have some kinda helpful advice, but nothing like Fakespot offered. https://www.reddit.com/r/firefox/comments/1ktm4g4/now_that_f...
If you use something else, have found a good alternative or a particular prompt you've tried in your favorite LLM to get info on an Amazon product, let us know!