I use AutoSleep/HeartWatch/AutoWake for sleep tracking and thinking about picking up a cheap S0 to use while sleeping. Will it do the job or will I need a newer generation one? I’ll switch to my S4 right after waking up.
Fortunately, I've kept my original S0 for this exact reason. It isn't worth much (maybe $25 at this point), so I figured I might as well keep it for sleep and also to use when I do yard work. It still tracks activity and sleep like a champ. Battery life is still good.
I did find sleeping with the watch slightly annoying though because the light would disturb my sleep at times when it would turn on and the watch was close to my face. Once I enabled tap to wake instead raise to wake... this solved my issue.
Of course, the watch's days are numbered as better apps come out that require WatchOS 5. Once that happens, I'll probably just keep the last version I have when I get a new watch in the future. For now, its S4 & S0 for me.
Charging is one reason and also because those watches are so cheap in my local market. I could probably pick one up for around $50. I’ve been considering buying a second charger too so that’s $20-$30 towards the S0 too. It’s effectively almost free.
I mean you could do it but why not use your S4? My S2 is on my wrist unless I'm in the shower or it's on the charger. With most all background refreshes turned off I can get at minimum a full day + on a charge. Go to bed at 100 power, wake up in the 80% range, back on the charger when I shower and repeat.