I did a survey where I blasted the use of these devices in direct sunlight. I believe my response was “useless”. Since then I acquired a 3M 98-0440-5210-2 Privacy Screen Filter from precision.com for $15.95 plus shipping. I had to cut it down with scissors but it sticks on & if your orient it correctly it works well enough to make a smart phone “useful”. It’s not perfect but does make a difference & finger touching still works fine. I also filed down both the power button & the level control button so I have to use my fingernail to use them thus eliminating their always getting pushed accidentally while hiking. I am a “thru” hiker (I’ve done the PCT twice, the CDT once & I will be finishing the PNT this year) & want to use BackCountry Navigator & my HTC Incredible instead of my Garmin.
BackCountry Navigator works so much better than my Garmin. The only issue is downloading maps which is too slow, but doable. I’m still trying to get Mobile Atlas Creator figured out but don’t have time now to deal with it.