I have avoided Prime as have a policy to always try and buy elsewhere if at all possible (except Kindle Books).
About a couple of hours ago, just googled trial period. It came up and logged in and accepted the free period. It also says it can be cancelled at any time - probably hard work though even when paying - so believe no fixed length contract??
Went to TV (3 yo Samsung Smart TV). The app didn't immediately work, but "Resetting" it by use of power switch and I now have it up and running ready for Saturday.