This gun would not be practical
TL;DR: Recoil and pure weight would make this gun very hard to handle and inferior to smaller arms
As other answers already covered the problems of the weight of ammo and heat produced, I will focus on recoil.
All of the following data comes from Wikipedia and assumes the slowest fire rate of 2000 bullets/minute of the M134 Minigun.
$F_{recoil,M134} = 0.011 \text{ kg} \cdot \frac{2000}{60\text{ s}} \cdot \frac{853\text{ m}}{\text{s}} = 312\text{ N} \approx 7.7 \cdot F_{recoil,AK47}$
So the recoil (nearly 8 times as high as that of an AK47 on full auto) of this thing will make it very unprecise and hard to handle, even when firing only in short bursts.
Also as it seems he has the magazine mounted directly to the gun, which would weigh in at approxiately 7 kg assuming it is loaded with 200 rounds. Holding a total of 12 kg attached to the lower part of the arm when holding it in front of the body like seen in the images will also prove quite exhausting.
Also delay and sound from spinning up will make it unusable for surprise attacks. The gyroscopic may also affect aiming but the effect should be negotiable compared to the issues with recoil.
Here is a video of a minigun with supposedly similar specs being fired from the hip:
https://youtu.be/d84r8gMGxFQ?t=145
It can be seen that it is possible to fire it, but only with a solid stance and an external magazine for longer firing times.
One could imagine a person carrying a 1000 round magazine in a backpack and and the gun on the hip like in the video but the low mobility due to weight and bulk would make this still an easy target.