I have an HTC One M8 running the latest Windows 10 mobile insider build. I have redeemed my free minecraft copy on my Microsoft account, and have downloaded it on my PC. The game is in my library when I check the store on my phone, but I cannot download it. The store tells me to check additional info, but looking there I cannot see what features my phone lacks.
Snapdragon 801 quad core x86 (I believe) processor
Adreno 330 GPU
2 GB RAM 1080p Display