It does appear that Amazon took both Echo Input and Echo Flex out of their website. Echo Flex was convenient that you can just plug it into the wall. But the built-in speaker was horrible. A pocket radio from 1980 sounds better than the Echo Flex.
Of all the devices that Amazon discontinued, I liked the Echo Buttons the best. I have 4 of them and I wish I could get some more. They make excellent triggers for Alexa routines. You press a button and your routine runs. I'm not aware of any other devices, Amazon brand or third party, that can do the same.