Anccer Premium Slim Case ($8)
The only brand on this list we've yet to try ourselves is Anccer. That said, the case looks similar to most quality options on the market, has a cutout for the microphone, and is very thin. For what it's worth, we see this brand often so buy with confidence.
Anccer is using a standard impact-resistant TPU material that's durable and lightweight. The case is matte black, but they have other options too. This should work with all features of the HTC U11. This case is thin, lightweight, and durable. That said, thicker cases will probably
Buy it Now on Amazon for $7.88 in Black or Smoke Gray