They may not be the first case maker that you look for, but after having used the spigen Slim Armor case for the HTC One M8, I would say that it should not be the last one you consider. Cases are a very personal and unique preference that people have. Some can be very pricey, depending on the level of protection and bling that you require. Others can be very reasonably priced, but are nothing more than wrapping paper to make your phone "look better".
The Spigen Slim Armor fits right below the tough/rugged armor category that Otterbox seems to fill so well. Upon opening the box, I was disappointed that the case didn't offer me the screen protection that I'm used to getting with the Otterbox, but I've quickly gotten used to that. I realize that by definition, the "Slim Armor" should be a more subtle, less bulky cover that might sacrifice protection for style and design. However, I'm quite comfortable now with the idea that I don't have to wrap my phone with a "bumpercar" style case that makes it feel more like a personal security device and less like a personal communications device!
My pics may not do it justice, but I can say with great confidence that this is the first case I've seen that seems to fit perfectly with the design aspect of the phone it was built for. When you have an Otterbox or even a Body Glove case on your phone, everyone knows that you are using a case by one of those manufacturers because they are distinctive. They LOOK like something else is on the phone. The Spigen LOOKS like your phone, or at least, on the HTC One HK edition it does. I've had people tell me that they think the phone is 'slightly' too big, but then when they realize I have a case on it, they ask two questions: 1) Did that come with the phone? and 2) What kind of case is that?
There is one drawback that I must point out, for those of you who actually use this feature. Unfortunately, the Spigen case designers did not consider the IR blaster on the M8. The case completely covers the IR blaster on the M8, and renders the Universal Remote Control function on your device un-useable unless you remove the cover. The cover is easy to remove, but it's the principle of having to remove the cover whenever you want to use the Remote that is a bother.
All the same, I would say that for the HTC One, it's well worth the investment, especially if you are looking for something that is aesthetically more appealing and in line with the phone OEM's design theme.
Disclaimer: The Product Ambassadors are Sprint employees from many different parts of the company that love technology. They volunteer to test out all sorts of Sprint devices and offer opinions freely to the Community. Each Product Ambassador shares their own opinions of these devices, therefore the information in this post does not necessarily reflect the opinions of Sprint. The PA's do not represent the company in an official way, and should not be expected to respond to Community members in an official capacity. sprintemployee.