PDAs like the Newton and Palm were great. They had two very obvious barriers that held them back. The first one was they weren't merged with a smart phone. I was a Newton developer and had conversations with people inside and outside of Apple about the need to merge the Newton with a smartphone. The second was lack of internet connectivity. I worked on some projects that involved using a cellular modem with the Newton. At the time it was very slow and very expensive. Just running our (brief) demo cost about $5 worth of data. In the case of the Newton specifically, I think there were looming security problems that would have been a nightmare if it had moved forward and had internet connectivity widely merged with it. The programming model made it easy to access any data on the device and even the internals of other applications. My main point, though, is that it was pretty obvious the kinds of super cool things you could do with PDAs if they had ubiquitous network access and integration with a phone. It isn't clear what technical limitations are in Smart Watches that prevent them from being significantly more useful. Perhaps the Apple Watch will be more useful if Siri becomes more useful and AirPods ever ship? I don't know. Its not that the watch isn't good, it is just that we haven't figured out what compelling use cases exist yet.