Firstly, let me state that HTC has a good smart-phone. Highly rated by consumers and techie reviewers alike.
Secondly, there are so many other aspects of a smart-phone besides how many pixels the camera has. That being said, using a cellphone to take useful pix can be of limited value. Of course, most of us that have them, use these cameras quite a bit when we need a quick snapshot - myself included.
Comparing an 8mpix cellphone camera over a 4mpix does not mean more is better. Pretty iffy comparison at best. What comes into play are issues like... How good is the lens, ability of the software to render sharp pix and how well it takes pix in less than ideal lighting. Of course, how well you can make clear phone calls, and use other online apps matters, too. Why not try them out first?
Here's a review of that camera:
"In regards to the smaller 4MP camera sensor, Whitehorn says that companies have been using megapixels as a marketing tool and that megapixel counts don’t actually mean much for consumers. By using 4MP, the HTC One offers enough megapixels for most mobile photographers and also brings in quality low-light photos to boot."