I purchased a subscription to one of the review import apps, and they told me it’s legal. I don’t want any trouble because of this.
The legality depends on what the publisher allows, Amazon in this case.
You could check their terms of service, but I would also reach out directly to Amazon support, so you can have proof to present in case you misinterpret the terms of service, or something changes in the future. If you have a case and screenshot showing an Amazon representative saying it’s ok to use their review content, that would help you in avoiding any penalties from Amazon.
That brings up an important point in operating a business - always go to the source of truth, don’t rely on opinions (in this particular case the app that gave you their opinion, also me haha… always go to the source to get the true answer that will alleviate any legal concerns).