If the envelope is time on it, very good edge and backside protection

The shell (as well as other third party) are very difficult to put on to the phone. It always slips out again a corner and you have already pretty to use force to get it in there. But the protection is good, if it's in there.
But because it's so hard to pull up only 3 stars. Build quality is good for the price and the HTC One phone looks in this transparent sheath very sophisticated and high quality from.