I placed an order for one of these immediately after receiving a Spigen Slim Armor last week...which is a beautifully made case in its own right, but just adds way too much bulk and weight to the phone. At first I wasn't that into the industrial look of the Unicorn Beetle, didn't think it matched the sleekness of the M8, but it grew on me, especially with how it highlights out the secondary camera.
Got the Supcase Unicorn Beetle today and I must say I'm very impressed by it. It looks really nice in person, especially with the faceted pinched in waist of the rear which visually is striking, and at the same time functionally helps to narrow the grip of the phone. I like how the sides are a matte TPU but still quite grippy, while the top edge is a glossy TPU to give it a bit of flash. It fits the M8 extremely well, quite a tight fit, but also feels way lighter and more form fitting than the Slim Armor. I have it combined with a tempered glass screen protector, and the end result is that there's not much of a lip left to put the phone screen down...it's just about flush.
My only gripe is just how dang sharp the openings are for the USB and headphone ports. I tend to use a pinky to help cradle the phone one handed, and my pinky lands right in those ports...and I can't help immediately feeling irritated by how sharp the edges are.