I have the Schuzthülle of Mumbi for my HTC One since about 3 weeks the shell fits snugly and leaves at the appropriate places recesses freely (eg camera, headphone jack, USB port, microphone and on / off switch). Unfortunately, the sheath covers the volume control, even if it can still be operated even without big problems.
I've never fallen off the smartphone fortunately, so I can not say anything about this protective function of the sleeve. Dirt or sweat keeps the envelope from the back panel, however. In combination with the protective film, which I had bought at the same time, the phone is protected from excessive wear.
Conclusion: A suitable, through soft case for the HTC One.
I hope I could help you with this review.