I've used Kobo's for navigation since 2013. I had two Kobo's before moving to a Kobo Glow. My first two Kobo's suffered from sun/heat fade. The second one being so bad I decided I had to upgrade. My newer Kobo glow does much better although suffers some fade too. It has a larger footprint than the original Kobo for better or worse.

I use an OTC USB cable to my S100 with good success. The mini USB has worn out after about 30 flights. The connection is now loose and creates issues requiring wiggling. I have a BlueFly vario hardwired for backup and that works without issue. The touchscreens have always been reliable for me

I highly recommend the Kobo Glo with Top Hat Soaring. The sunlight readable screen is unmatched. You can find Preloaded Kobo's with GPS and XCSoar on eBay.