Talking with a user on Reddit I'm wondering if I went too easy on the magnetic base. To clear some things up I found the magnet too weak to stay in place under pressure. However, the bottom of my case has a fan mounting location and I'm not sure how much this affects the magnets ability to grip the case. Towards the end of the video I mention that I used zip ties to better secure the base of the brace.
In future versions of this brace I'd like to see it heavier with a wider base and stronger magnet. I'd also like to see the thumb screws for the fingers/clamp a little longer.
Overall however I'm happy with my results. My gpu is no longer sagging and looks much better because of it. I'm no longer worried about my gpu becoming damaged from sag.