To be honest the only two reasons we can recommend anyone get the HTC U Ultra is the big display (or design) and the camera. Everything else has us confused as to why HTC chose what they did. Even then, the camera is slightly better than the Pixel. Samsung, Apple, LG and Google all have big things coming in 2017 that will likely top it.
Moving on to our first, and perhaps biggest reasons not to buy the HTC U Ultra -- Battery Life.
HTC went with a huge 5.7-inch Quad HD screen and a second screen that will require lots of power. But for whatever reason HTC went with a 3,000 mAh battery. In today's standards, that is small. Compared to the Galaxy S7 Edge with 3,600 mAh, OnePlus 3T with 3,400 mAh or Google Pixel XL with 3,450 mAh all powering a smaller 5.5-inch screen.
Samsung arguably makes the best smartphones. In 2016 their phone with the worst battery life was the Galaxy S7 at 3,000 mAh. It has a 5.1-inch display. The Galaxy Note 5 from 2015 had a 3,000 mAh battery and Samsung quickly learned from that mistake. HTC apparently missed the memo.
Potential buyers looking to get a huge and powerful flagship phone that intend to fully take advantage of all it has to offer -- like two screens -- won't be able to last all day with just 3,000 mAh. The HTC U Ultra battery isn't big enough for 2017 standards.