Is this a real and good Rechargeable battery pack replacement?

Not saying you do this. Just a tip: To extend the battery life of batteries always use then till they are flat, then charge them. Constantly charging them with energy in them can shorten the lifespan.

I bought the Nyko one for my Xbox One controllers and it works fine.

Clearly doesn't use the official charge cable. I've always been a bit leary of cheap third party items like this, I say avoid it.

I've had a couple of Nyko batteries for over four years and they are just now being to lose charge capacity. I can still go for days without charing and they do work with the MS charging cord.

Rechargeable batteries are the way to go like those posted above me. I use duracell AA rechargeable batteries for my controllers and AAA Duracell batteries for my wireless headset. When they go flat I just put them on charge and put a backup pair in.