I am not sure if I should feel lucky or foolish but The Apple Watch I use everyday is the same watch that I bought the day it launched, commonly known as the Series 0. This watch has been worn all day every day since I bought it and it still looks good as new. I also perform a workout while playing a podcast every day and the battery life is still acceptable. Aside from wanting a new one there is no current reason for me to need a new Apple Watch.
When I started developing for Watch OS4 the performance was almost useless for the Series 0, not just for the Watch Kast app but many others too. Transfers were often cancelled and apps crashed constantly. Most of the problems did not happen on the newer, more powerful watches so I knew my application was fundamentally sound. Strangely enough there were no issues with audio playback or performance during workouts it was limited to file transfer, saving files, and animations in the app. This version makes many of the under the hood operations more efficient and with subsequent updates to the operating system Watch Kast now performs better than before even on the Series 0 watch. So, any of you having issues with older watches please be patient and things will sort themselves out.
I would also like to add that best file transfer times are when both the iPhone and Watch are on their chargers. Up to 100b files should only take a few minutes to arrive. I am also working on a file syncing solution that just might work this time but more on that later.
You can download Watch Kast from the link below. It will be on sale until mid November for just 99 cents.