It’s very freeing to have low standards.- Caroline Haskins
In my quest for the quantified self I go the La Roche-Posay UV Tracker and my basic summary is, don't get it. I'm sad to say that this product is a dud for a reasons. Many years ago I had this great app on my phone (made by a sunscreen company) that would ask for your skin type and then you start a "sun session" and it would get the UV index for your location and remind you periodically to reapply sunscreen. Simple. Awesome. Haven't found one since. I am sort of wondering if I could recreate it as a Siri Shortcut... but for now.
This itty bitty tracker can be worn anywhere with sun exposure and I wear mine on my Apple Watch wrist band. Everywhere I have tried to wear it (shirt color, watch band, hand brim) has had it slip off at one time or another. I'm certain I'm going to lose it one of these days. I have lost it for days at a time only to find it in a kid's bed or the floor of the car.
The device syncs data over NFC (not Bluetooth LE) so that means the phone doesn't get any updates unless you launch the app hold the phone up to the device and wait a few seconds. The App sends a push notification every couple of hours, "you should probably sync data again." It's incredibly inconvenient and really needs to be like all my other smart trackers that just magically send data to my phone so my phone can hit me with useful alerts.
The app itself just tracks exposure and doesn't have any smarts to remind you to reapply sunscreen or do anything fancy. So I just get to see that I've been exposed to "242%" of my daily allowance, but there is nothing to let me know if that is okay because I was wearing SPF15 most of the day or not.
Anyway, it's silly and I don't really see any market for this thing other than silly people like me.