I'm setting up a canon 7Dii to record wildlife. I'll be shooting with an original 100-400 lens. One day I'll upgrade to the Mark II version lens. I'm all set up with tripod, fluid head and ND filter. Will be getting a screen loupe. When looking into buying an HD screen to help with focusing, I came acrossed the Atomos Ninja 2 and Blackmagic Video Assist, which I thought would be a good screen and also have added benefits of improved IQ, but after watching a number of reviews, I'm not so certain.

I'm new to video. I've not been able to find any data regarding image output quality for the 7Dii; such as 4-2-2 or 4-2-0. Not even sure if that matters. All I know is that the camera shoots MP4. Can I expect one of these external recorders to improve the IQ of the 7Dii. Will it be anywhere close to IQ of the video seen on TV nature shows. Will it be the highest quality that I can expect to get with a DLSR and existing lens? Better options?

Also, is there any advantage to shooting with a hard drive, like you do with the Atomos, versus SD card used with the Blackmagic?
I have no expectations of shooting long clips, probably no more than a few minutes at a time. My workflow isn't rushed?

Thanks.

You will not see a difference between footage you record internally on your 7D Mark II and the Ninja 2 or Video Assist.