I purchased this screen protector from a Best Buy store nearly a month ago, one week after purchasing my Apple Watch Series 1. When I got home, I immediately put the screen protector on, and in the process of putting it on (which is no easier or more difficult to do than other screen protectors), I scratched the screen protector (no harm to my watch, but the screen protector was really useless). On top of that, I realized that I had purchased a 38mm screen protector instead of the appropriate 42mm, and it seemed as if everything that could go wrong did; however, I contacted ZAGG customer support, and they were extremely helpful and provided me a free shipping code for a warranty replacement (and they let me get a 42mm with no penalty!) After receiving the replacement, I sent the old one back and have had absolutely no complaints with this one. When you put it on, be sure you get the edges on and don't wipe on it too much after you take the installation cover off - small air bubbles will go away within 24 hours (faster if you walk around in the sun for an hour or so), and if you rub too much, you could scratch it.
As for the appearance, you can't really tell that it is on until you touch it (or look really close for it). It doesn't seem to reduce touch sensitivity by a largely noticeable amount, and it seems very slim. And, if by chance something happens to it (which it will, eventually anyway), ZAGG will replace it for a $5.99 shipping charge (or free if it is a special circumstance).
If you are looking to buy a screen protector for your Apple Watch, get this one - you get what you pay for in the quality and the service of ZAGG. Even though $15 seems high, it is worth it to have the peace of mind knowing that my Apple Watch screen won't be scratched!