Sadly after just under a year the screen fell off my Nike Series 2. In fact it wasn't a case of the glue, or battery .. but physical damage. I'm pretty careful but I must have managed to knock it against something and the glass shattered. I did also drop it onto a tarmac drive from a height of about 0.7m . Also possible. Even though I had a screen protector -- but that only covered the top surface and the knock must have been sideways
Fortunately I had insurance and the watch is replaced, but I now have a protector which is both a plastic lip and glass cover. I personally feel the watch is a little susceptible to sideways knocks in particular as there's no metal bezel. I doubt there's any difference between the SS and Aluminium in this regard. Sapphire glass may be more scratch resistent, but I don't think it's any tougher for impact.
I should add that the (bank-arranged, non apple) insurance company first 'fixed' the watch incorrectly. The NFC didn't work, and I bet you it wasn't waterproof. FOrtunately upon complaining they replaced with a brand new one ...
TBH It's shattered my confidence in durability somewhat, so I now tend to take off the watch a little more (though one could argue this is one of the most likely times you could drop it!). That being said the utility is superb, so I'd probably do the same again, albeit always making sure I had insurance (I now have taken out apple care + for accidental damage) and a wrap around protector. I kinda wish for a slightly more traditional metal bodied design like numerous android wear watches (I actually had a moto 360. Better in that regard but frankly android wear is rather naff)
