Sharing my experience after 3 days with a fully coated Apple Watch from Mobile Outfitters and my advise is - Coat the front and sides, ceramic back is optional but do not coat the heart rate sensor.
- All was fine on the first day right after I coated it, but after awhile it felt uncomfortable, the watch stuck to my skin and it was tugging at my bulu lol Thought it was too tight so I loosened it but it was worse wearing it loose, it was rough and it rubbed my wrist with friction and caused irritation. Thought I wasn't wearing it right so just shrugged it off took it off and ended the day.
- Second day wore it to the gym and after a few reps, my goodness it felt so sticky and hot on the wrist. Super rough and grimy. Started pulling at my wrist bulu badly. The irritation was horrible as well. Got pissed and ripped off the film on the heart rate sensor, cleaned it a bit and put it back on. And my goodness it was like I just put on a different watch.
- Third day - after a whole day and I felt like I could leave the watch on my wrist forever.
The coating is just like your phone non tempered glass regular screen protector. It can be abrasive on your wrist especially when it gets sticky from your sweat or wrist heat. What is more I believe the film traps heat as well. Also my regular heart rate readings were consistently 10+ BPM higher than after I had the film removed from the heart rate sensor, so the film might affect accuracy somewhat. There is a longer pause as well before your watch starts charging after attaching the charger.
Now with the sapphire back touching my skin, it feels so much cooler and the watch slides around effortlessly with no friction if I decide to wear it a little looser and able to adjust the position of the watch from time to time. Bulus were no longer harmed. Watch also starts charging almost immediately after attaching the charger.
I am considering taking out the layer on the ceramic back as well now. The heart rate sensor and the entire ceramicback really do not need any coating in the first place tbh. Sapphire glass and ceramic are incredibly scratch resistant. Plus those parts will be on your wrist most of the time anyway.
TLDR - Get the front and the sides coated will do. Ceramic back, optional but the heart rate sensor is a major no go for coating. You might even get a cheaper price with only the front and sides coated. The front and side coating did come in handy once for me yesterday when I accidentally hit either the side or front screen of the watch when trying to stop a lift door from closing when I was rushing. I'm convinced there would've been at least some scratches had it not been for the coating.
Thanks for the great advice. I am thinking whether should I help my wife to coat the watch or not. I think I will just go with the sides and front.