Amazon Echo - 3rd Generation just as good as 4th generation? Only for AUX output.

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Just picked up a zenith stereo console and l am planning on hooking up an Amazon Echo to the AUX inputs. The Echo Flex looks like it may work for what I need but thinking of putting it "on top" so it can hear my commands better "if needed". I'm also seeing that the Flex is "not currently available" at Amazon so maybe they have a new model coming out? That being said the 3rd generation "DOT" appears to be slightly smaller (and compact) compared to the 4th generation so if I hide it behind the console or TV it might be best to grab a 3rd generation.

Any input?