I’ve found Siri on Apple Watch massively useful. On the phone I’ve always felt Siri was little more than a novelty but on Apple Watch I use Siri a lot — changing tracks on Apple Music (especially useful in the car or when playing through bluetooth speakers), controlling my Hue lights or even setting quick reminders.
But I do agree with M.G. Siegler, speed is a bit problem with Siri on the watch.
Amazon Echo isn’t out in the UK so I could be wrong but my thoughts are why have a stationary assistant when I can have one with me at all times on my wrist.