As far as I know, the HTC One M8 is not officially supported anymore. You are running the November Update, or Threshold 2 (TH2) which is the minor update following the initial update of Windows 10 (TH1). I'm not certain if it's Microsoft's or HTC's fault, or if it's a combination of both, but I do know that your phone will not receive anymore updates besides the occasional cumulative update. And even that is an "if."
It's unfortunate because it was a great phone and if HTC had shown any care for the device it could still be a great phone. But without official support I can't really recommend it to anyone.
You can take a look at the Alcatel Idol 4s which for you I think would be a great alternative option. It's a beautiful, well built phone with a lot of power behind it and it is officially supported.