I watched Greyhound in 4K HDR 10 bit( an 18 GB file) in my MI box 4k two weeks back. Playback was good and without stutters in Kodi. I watched Avatar 4k HDR 10 bit(a 22 GB file) before that via the box. No issues.
If you do fast forward or fast backward, then sometime the screen stops(maybe once in 10 attempts) and you need to press the forward or backward button once again to get going.
I have not experienced Shield Pro but going by the reviews and feedback, it's simply a lot better than MI box - probably the best within 30k. Even Zidoo is a good one. But, if someone is looking for an alternative which costs 8 times less due to price or availability factor of the Shield, MI box 4K is a decent one at 3.5k.