First of all, what's this M9 smartphone all about? If you're familiar with the HTC M8, there's a lot of common denominators here. For one, the HTC One M9 has the same 5-inch 1080p LCD display, and the same all-metal design. The location of the sensor, camera, and speaker are all the same as the M8 (except, the M9 now has just one rear camera instead of the Duo). So, basically you're looking at twins from first glance. The only physical different includes the way the edges of the phone are more defined than smooth. Overall, this is a very elegant looking Android device. It might remind you of the iPhone.
Powered by a 1.5GHz Qualcomm octa-core Snapdragon 810 processor, the HTC One M9 has Adreno 430 graphics, comes with 3GB of RAM, and 32GB of storage (expandable via microSD) (PC Mag). Battery life is said to be a bit better than the M8, as it made a 240mAh jump up from 2600mAh to a 2,840mAh battery. However, regular use still requires a charge by the end of the day, meaning not much improvement.
Onto the HTC One M9+. According to BGR, known differences include a larger 5.2-inch to 5.5-inch (different rumors) quad HD display, a faster 2.0Ghz processor (MediaTek or Snapdragon 810, depending on the region), the return of the rear-facing Duo Camera, and a fingerprint scanner- thanks to leaked photos. Prices for this device is unknown. However, considering the One M9 is said to go for 580 Euros SIM-free, we can expect all those One M9+ upgrades to cost a pretty penny.