You CAN run some form of autoblock below the Safeguard.
MadRock specifically states that you should NOT do this, so do your own research.
My understanding is that it is not recommended because if you tie the autoblock too long (or run a short bridge), the autoblock cord can get lodged in the Safegaurd and you would be stuck in the tree if you didn’t have a way to unweight the system.
I DO run an autoblock in the form of a Beal Jammy tied in a Klemheist below my Safeguard.
I always make sure that the autoblock catches a few inches before it reaches the Safeguard. I also carry at least one 120cm climbing sling that can be used as a foothold to take the weight off of my mainline if my system ever jammed up.
I have used the Safeguard hundreds of times without a backup and never had a problem.
However, I did have one experience where I was using a figure 8 without backing it up. Long story-short, the figure 8 released suddenly. I didn’t hold on with my brake hand. I panicked. I fell about 12’ flat on my back. So, for me, I don’t 100% myself to release the handle in a critical situation.
^^ you can see my autoblock in the bottom right of this picture.