They've worked for me, I would just go with the 3, not the one with the screen. Mine was always very consistent, and boy can it shock you.

My S/O at the time hated me cause I can sleep through everything, so the watch was the only sane option for the both of us, an it did wake my ass up. Can't say I've ever trained myself to wake up at 6am normally though lol.

Define "work", do they actually zap you, vibrate, beep? Absolutely! Oh, did mean if you ask it to do something it will do it reliably and when you asked it to? Nope!

I used one for a bit as a silent alarm to take medication in the middle of the night and not wake up my wife. Did that alarm ever consistently go off? Nope! The app you use to interact with it is hot garbage and feels like it was contracted out to get it to "it technically works" and just kept getting crap piled on.